# JESSICA

Most popular questions and responses by JESSICA-
## Chemistry

Classify the possible combinations of signs for a reaction's ∆H and ∆S values by the resulting spontaneity. A) Spontaneous as written at all temperatures. B) Spontaneous in reverse at all temperatures. C) Spontaneous as written above a certain

*asked on November 9, 2011* -
## Science ~CHECK MY WORK PLEASE~

A scientist is trying to determine the identity of an element. It is highly reactive in water and forms an ionic bond with chlorine. It is also very shiny. The element is likely A. From Group 17 ********** B. From Group 1 C. From Group 15 D. A Noble Gas

*asked on January 28, 2014* -
## Chemistry

How many grams of dry NH4Cl need to be added to 2.10L of a 0.600M solution of ammonia,NH3 , to prepare a buffer solution that has a pH of 9.00? Kb for ammonia is 1.8x10^-5. I just wanted to make sure I dd this write, can you please check my work? Thank

*asked on October 8, 2011* -
## english

What elements of the Restoration comedy are seen in The Importance of Being Earnest? (5 points)

*asked on April 25, 2012* -
## help plzzz

ALGEBRA PIZZAZZ: IN MUSIC, WHAT DOES "ALLEGRO" MEAN?

*asked on December 3, 2008* -
## Math

A camper attaches a rope from the top of her tent, 4 feet above the ground, to give it more support. If the rope is 8 feet long, about how far will the stake need to be from the middle of her tent?

*asked on December 27, 2017* -
## physics

A spring has an unstretched length of 10 cm . It exerts a restoring force F when stretched to a length of 12 cm . For what total stretched length of the spring is its restoring force 3F? At what compressed length is the restoring force 2F? I keep doing

*asked on April 11, 2016* -
## Physical Science

A bicycle and its rider together have a mass of 80 kg. If the bicycle's speed is 6m/s, how much force is needed to bring it to a stop in 4 seconds

*asked on February 1, 2012* -
## Calculus

A particle moves along line segments from the origin to the points (3, 0, 0), (3, 3, 1), (0, 3, 1), and back to the origin under the influence of the force field F(x, y, z) = z2i + 5xyj + 4y2k. I have tried multiple times to solve this problem but the

*asked on December 8, 2014* -
## Chemistry

Two 20.0-g ice cubes at –20.0 °C are placed into 295 g of water at 25.0 °C. Assuming no energy is transferred to or from the surroundings, calculate the final temperature of the water after all the ice melts. Heat capacity of H2O(s)=37.7J Heat capacity

*asked on June 27, 2013* -
## Geometry

Two similar triangles have a scale factor of 3 : 5. The altitude of the larger triangle is 24 inches. What is the altitude of the smaller triangle?

*asked on May 16, 2016* -
## Science

When evolution was first proposed, which of the following was used as evidence to support the idea? 1.observations of nature 2.laboratory experiments 3.extensive fossil collections 4.genetic sequences I think its either 1 or 4

*asked on October 29, 2014* -
## English

(I just need 2 writer ideas) In the middle of the 19th century, political philosopher Alexis de Tocqueville claimed, "The inhabitants of the United States have...properly speaking, no literature." In other words, de Tocqueville believed that America’s

*asked on January 7, 2015* -
## chemistry

a)H2SO4 b)CuS c)HF d)Zn(NO3)2 Which are strong, weak, or non electrolytes. I was think A was strong B and C were weak and D is non

*asked on October 5, 2011* -
## Chemistry

Refer to the following equation: 4NH3 + 7O2= 4NO2 +6HO, How many moles of ammonia would be required to produce 11.9 mol of water? Can you please walk me through the steps on how to figure this problem?

*asked on March 16, 2012* -
## English

The title "another evening at the club" is close in meaning to "just another evening at the club" given the events of the story, what is the significance of this meaning? I need help explaining this. I have no idea how to word it

*asked on June 16, 2016* -
## chemistry

What is the major difference between the two-dimensional and three- dimensional models of ethane and methane? When might you choose to use a two-dimensional model rather than a three-dimensional model when representing one of the molecules?

*asked on September 30, 2013* -
## Chemistry I - University Level

Suppose 5.87 g of barium acetate is dissolved in 300. mL of a 71.0 m M aqueous solution of sodium chromate. calculate the final molarity of barium cation in the solution. You can assume the volume of the solution doesn't change when the barium acetate is

*asked on September 27, 2015* -
## Pre-Algebra

The grocery store sells kumquats for $4.25 a pound and Asian pears for $2 a pound. Write an equation in standard form for the weights of kumquats k and Asian pears p that a customer could buy with $12.

*asked on April 25, 2012* -
## math

In Philadelphia the number of hours of daylight on day t (where t is the number of days after Jan. 1) is modeled by the function L(t)= 12+2.83sin(2pi/365(t-365)) A) Which days of the year have about 10 hours of daylight? B) Which days of the year have more

*asked on August 13, 2011* -
## Math/Algebra

On Dolphin Beach, the high tide is 2.2 meters and only occurs at 12 a.m. and 12 p.m. The low tide is 1 meter and only occurs at 6 a.m. and 6 p.m. Which function models the height of the tide t hours after 12 a.m.? a. h(t)=0.6cos(πt/6)+1.6* b.

*asked on April 8, 2018* -
## Geometry

What does the diameter of a sphere join? any two points on the sphere any two points on the sphere and contains the center

*asked on February 24, 2016* -
## Math

The planet Mercury is approximately 6 x 10^7 miles from the Sun. The distance between the Sun and Mars is approximately 2 x 10^8 miles. ABOUT how many times farther from the Sun is Mars than Mercury? 2 3 20 30 I got B? Can you please check? Thank you!!

*asked on December 27, 2017* -
## Physics

Two hockey pucks of equal mass are involved in a perfectly elastic, glancing collision, as shown in the figure below. The orange puck is initially moving to the right at voi = 3.95 m/s, when it strikes the initially stationary blue puck, and moves off in a

*asked on November 6, 2016* -
## AP Chemistry

(a) When 300.0 milliliters of a solution of 0.200 molar AgNO3 is mixed with 100.0 milliliters of a 0.0500 molar CaCl2 solution, what is the concentration of silver ion after the reaction has gone to completion? (b)Write the net cell reaction for a cell

*asked on April 5, 2010* -
## Chemistry

The energy used to power one of the Apollo lunar missions was supplied by the following overall reaction: 2N2H4 + (CH3)2N2H2 + 3N2O4 -> 6N2 + 2CO2 + 8H2O For the phase of the lunar module ascended from the surface of the moon, a total of 1200kg N2H4 was

*asked on February 6, 2011* -
## Organic Chemistry

Separation scheme for isolating benzoic acid Could you please show me a separation scheme for isolating benzoic acid from a reaction mixture if mixing a Grignard reagent phenylmagnesium bromide with dry ice (CO2) in ether? Thanks!

*asked on October 22, 2010* -
## Science

The force of gravity of objects on the moon is approximately one-sixth of their value on Earth. Joe weighs 7633 N on earth. What will Joe's mass on the moon be?

*asked on February 10, 2017* -
## Physics

Two blocks of masses m1 = 2.00 kg and m2 = 3.70 kg are each released from rest at a height of h = 5.60 m on a frictionless track, as shown in the figure below, and undergo an elastic head-on collision. (Let the positive direction point to the right.

*asked on October 29, 2012* -
## Algebra

A can of soda is placed inside a cooler. As the soda cools, its temperature T(x) in degrees Celsius is given by the following exponential function, where is the number of minutes since the can was placed in the cooler. T(x)=-22+44e^-0.03x Find the initial

*asked on June 15, 2011* -
## anatomy

where are the shoulders relative to these parts? 1. throat (inferior) 2. hip (superior) 3. ears (inferior) 4. hands (superior) 5. eyes (inferior) will someone please take a look at my answers and tell my if i am right

*asked on August 19, 2011* -
## physics

In designing rotating space stations to provide for artificial-gravity environments, one of the constraints that must be considered is motion sickness. Studies have shown that the negative effects of motion sickness begin to appear when the rotational

*asked on December 19, 2010* -
## Chemistry

When a 3.80 g sample of magnesium nitride (MW 101g/mol) is reacted with 3.30 g of water, 3.60 g of MgO is formed. What is the percent yield of this reaction? Mg3N2 + 3 H2O --> 2 NH3 + 3 MgO

*asked on November 2, 2016* -
## chemistry

A sample of propane(c3h8)has 3.84x10^24 H atoms. a) how many carbon atoms does the sample contain? b) what is the total mass of the sample?

*asked on January 15, 2011* -
## Math, algebra!! Please help!!!!!!

Using the numbers 5, 8, and 24, create a problem using no more than four operations (addition, subtraction, multiplication, division, square, square root, cube, cube root) where the solution will be an irrational number. Explain why the result of your

*asked on November 13, 2012* -
## Physics

A student sits on a rotating stool holding two 3.4-kg objects. When his arms are extended horizontally, the objects are 1.0 m from the axis of rotation and he rotates with an angular speed of 0.75 rad/s. The moment of inertia of the student plus stool is

*asked on November 27, 2012* -
## Pre-Calc

The Greek mathematician Eratosthenes (ca. 276-195 B.C.) measured the circumference of the earth from the following observations. He noticed that on a certain day the sun shone directly down a deep well in Syene (modern Aswan). At the same time in

*asked on March 16, 2012* -
## language arts

Which question should you ask during your third read of the multi draft reading process

*asked on February 5, 2019* -
## PHYSICS!!

Squids and octopuses propel themselves by expelling water. They do this by taking the water into a cavity and then suddenly contracting the cavity, forcing the water to shoot out of an opening. A 6.50 daN squid (including the water in the cavity) that is

*asked on April 11, 2016* -
## Can someone check these answers...

1. Which of the following events caused immigrants to migrate north after the civil war? -the passage of the homestead act****** -the emergence of industry in cities -advances in the printing industry - the completion of the transcontinental railroad 2.

*asked on November 9, 2012* -
## Math/Algebra

The equation yˆ=−6.2x2+41.5x−5.6 approximates the average number of cars that pass through an intersection x hours after 3:00 p.m. What is the best estimate for the average number of cars that pass through the intersection at 5:30 p.m.? a. 35

*asked on April 8, 2018* -
## History

magine you work in a steel mill in a large industrial city in England in the late 1800s. You live in a neighborhood with other factory workers, and share the same living and working conditions they do. Write a letter to your representative in Parliament

*asked on March 16, 2016* -
## History

2. In the space below, create a simple time line that traces the emergence of a constitutional monarchy in England during the seventeenth century. It is not necessary to include exact dates, but events should be in the correct order. Include at least eight

*asked on February 12, 2016* -
## math

Suppose you have $60 to buy shrimp and chicken wings for a party. Shrimp costs $10/lb and wings cost $6/lb. Write and graph a linear equation that could be used to determine the number of pounds of each food that can be purchased with $60 Would I start

*asked on November 5, 2015* -
## Chemistry

What mass in grams of a 0.500 m(molal) solution of sodium acetate, CH3CO2Na, in water would you use to obtain 0.200mol of sodium acetate?

*asked on February 2, 2014* -
## Chemistry (Regents level)

1- In the reaction Fe2O3 + 3 CO = 2 Fe + 3 CO2, what is the total number of moles of CO used to produce 112 grams of iron? a) 1.0 b)2.0 c)3.0 d)4.0 2- Given the reaction: 4Al + 3O2 = 2Al2O3 How many moles of Al2O3 will be formed when 27 grams of Al reacts

*asked on February 23, 2008* -
## Chemistry

Calculate the enthalpy change for: C2H4(g) + H2 --> C2H6(g) delta Hrxn: H2(g) + 1/2O2 --> H2O (l) C2H4(g) + 3O2 --> 2H20(l) + 2CO2(g) C2H6(g) + 7/2O2(g) --> 3H20(l) + 2CO2(g) I know I have to flip the third reaction but I don't know what to do next

*asked on October 29, 2014* -
## Science

Which of the following distinguishes living things from nonliving things? A) Living things are made up of cells;nonliving things are not B) Living things are made up of atoms;nonliving things are not. C) Living things are made up of elements;nonliving

*asked on October 20, 2017* -
## Math :(

Gil rolls a number cube 78 times. How many times can he expect to roll an odd number greater than 1??

*asked on April 30, 2012* -
## Chemistry

Identify the oxidation-reduction reactions among the following: 1. Zn(s) + Cu2+(aq) → Zn2+(aq) + Cu(s) 2. 2Na(s) + Cl2(aq) → 2NaCl(s) 3. 2Mg(s) + O2(g) → 2MgO 1 and 2 only 2 and 3 only 1 and 3 only All of 1, 2, and 3 None of 1, 2, and 3

*asked on October 2, 2016* -
## AP Biology

Assume that a particular genetic condition in a mammalian species causes an inability to digest starch. this disorder occurs with equal frequency in males and females. In most cases, neither parent of the affected offspring has the condition. (a) Describe

*asked on January 8, 2010* -
## Math

A triangle and trapezoid share a 15 inch base and a height of 10 inches. For what values of b is the area of the trapezoid less than twice the area of the triangle?

*asked on October 3, 2011* -
## chemistry

You have a sample of gas at -30 C. You wish to increase the rms speed by 12%. To what temperature should the gas be heated?

*asked on November 10, 2009* -
## Physical Chemistry

A saturated solution of Na2SO4, with excess of the solid, is present at equilibrium with its vapor in a closed vessel. (a) How many phases and components are present? (b) What is the number of degrees of freedom o the system? Identify the independent

*asked on October 3, 2015* -
## HISTORY

10. Which of the following statements is true regarding the Korean War? A. Stalin approved the North Korean attack in advance. B. Stalin was outraged by the North Korean attack on South Korea. C. Both Stalin and Mao expected the American response to the

*asked on September 3, 2012* -
## English

What is moral lesson in Annabel Lee?

*asked on November 16, 2014* -
## College chemistry math ratio problem

Earlier you determined that the proper ratio of packages of buns, packages of patties, and jars of pickles is 3:2:4. If you want to feed at least 540 people, but also maintain the proper ratio, what minimum number of packages of buns, packages of patties,

*asked on September 2, 2013* -
## math PLEASE HURRY

there are 24 students in a science class. Mr. Sato will give each pair of students 3 magnets. So far, Mr. Sato has given 9 pairs of students their 3 magnets. homw many more magents does Mr. Sato need so that each pair of students has excatly 3 magnets.

*asked on November 8, 2011* -
## maths!

the formula h=15t-5t^2 gives the height 'h' metres of a ball, 't' seconds after it is thrown up into the air. (i) find the times when the height is 10m (ii) after how long does the bal hit the ground? ive figured out that the answer to (i) is t= 1 or 2 by

*asked on August 6, 2008* -
## Chemistry

Addition of which of the following substances will increase the solubility of CuCO3 (s) in water ? CuCO3 ---- Cu^2+ (aq) +2 CO3^2- (aq) 1. Aqueous hydrochloric acid 2. Aqueous sodium carbonate 3. Solid copper (II) carbonate a) 1 only b) 2 only c) 3 only d)

*asked on April 4, 2012* -
## Physics university

In a tennis match, a player wins a point by hitting the ball sharply to the ground on the opponent's side of the net. If the ball bounces upward from the ground with a speed of 17 m/s , and is caught by a fan in the stands with a speed of 12 m/s , how high

*asked on October 12, 2009* -
## Math

If m and n are integers, which of the following must be an even integer? A. 2mn B. mn C. mn+2 d. mn-2 e. 3mn

*asked on August 25, 2015* -
## Science Check answers

2) What phenomenon naturally warms Earth's lower atmosphere and surface? • the formation of sunspots • changes in the shape of Earth's orbit • global warming (MY ANSWER) • the greenhouse effect 3) Which of the following is an example of human

*asked on April 29, 2016* -
## Physics

A 57 kg boy and a 45 kg girl use an elastic rope while engaged in a tug-of-war on a frictionless icy surface. If the acceleration of the girl toward the boy is 1.5 m/s2, determine the magnitude of the acceleration of the boy toward the girl. Answer in

*asked on October 14, 2012* -
## Chemistry

I did a lab the other day where we separated a mixture of NaCl, SiO2, and CaCO3. The Mixture was made by my professor and we did not know the original amounts of each compound. After recovering all of the compounds we found that there was.. 36.4% NaCl

*asked on February 4, 2014* -
## Chemistry

The density of aluminum is 2.70g/cm3. If a cube of aluminum weighs 13.5 grams whatis the length of the edge of the cube. I need help with the formula to figure this one out.

*asked on June 1, 2011* -
## math

A square pyramid has a surface area of 202 ft2 and a base area of 53 ft2. What is the lateral area of the pyramid? A.149 ft2 B.96 ft2 C.174 ft2 D.151 ft2

*asked on July 1, 2012* -
## Physical Science

A 3-kg stone is dropped from a height of 100 m. Find its kinetic and potential energies when it is 50 m from the ground.

*asked on February 17, 2012* -
## physics

A 200g mass attached to a horizontal spring oscillates at a frequency of 2.0 Hz. At one instant, the mass is at x= 5.0cm and has v= -30cm/s. find amplitude

*asked on February 3, 2012* -
## college chemistry

Please identify the net ionic equation for Na3PO4 +ZnSO4=Zn3(PO4)2+ Na2SO4

*asked on September 27, 2010* -
## Chemistry

You prepare a solution from 10.0 mL of 0.100 M MOPS buffer (3-morpholinopropane-1-sulfonic acid) and 10.0 mL of 0.071 M NaOH. Next, you add 1.00 mL of 1.89 × 10-5 M lidocaine to this mixture Denoting lidocaine as L, calculate the fraction of lidocaine

*asked on March 27, 2013* -
## chemistry

The Ka of hypochlorous acid (HClO) is 3.0 × 10-8 at 25°C. Calculate the pH of a 0.0385-M hypochlorous acid solution? i got help with this problem, but i don't get where one of the numbers came from (3.4 x 10^-5)??? i tried makeing 3.0 x 10^-8 the x but i

*asked on November 23, 2010* -
## Pharmacy calculations

Based on the formula below, what quantities of each are needed to make 180 ml of this lotion? Benzyl Benzoate 250 ml Triethanolamine 5 ml Oleic Acid 20 ml Purified water to make 1000 ml

*asked on June 27, 2018* -
## math

write the number of permutations in factorial form.then simplify. how many different ways can you and four of your friends sit in the backseat of a limousine? A)4!;24 B)4!;120 C)5!;120 D)5!;720

*asked on June 5, 2014* -
## Science

How does a nuclear power plant produce energy? A. Through solar panels B. Through nuclear fission reactions C. Through geothermal heat D. Through nuclear meltdown reactions I am not really sure what the answer is but I am thinking…c? Or I guess d?

*asked on April 13, 2017* -
## Science

A father swings his child around in a circle. The source of the centripetal force that keeps the child moving in a circle is _____. tension friction weight gravity

*asked on May 21, 2010* -
## American Government

1. Thomas Hobbes and John Locke were European philosophers who influenced American founding documents with which theory? A. social contract theory B. divine right of kings theory C. no taxation without representation theory D. equal pay for equal work

*asked on September 19, 2016* -
## Calculus

BoxedNGone truck rentals calculates that its price function is p(x)=160-2x,where p is the price (in dollars) at which exactly x trucks will be rented per day. Find the number of trucks that BoxedNGone should rent and the price it should charge to maximize

*asked on November 9, 2014* -
## math

use inductive reasoning to determine the units digit of the number 2^44 the unit digit of 2^44 is_____ powers of 2- 2^1=2 2^2=4 2^3=8 2^4=16 and so on that last one they have is 2^12 so 2^44 would be 1.7592188?

*asked on June 2, 2015* -
## math

below are the results of tossing a number cube 8 times find the experimental probability of tossing an even number. 3,4,1,2,5,1,6,5 1. 1/4 2. 3/8 3. 1/2 4. 5/8

*asked on June 5, 2014* -
## math

a customer went to a garden shop and bought some potting soil for 17.50 and shrubs. if the total bill was $71.00, how much did each shurb cost if they all cost the same? write and solve an equation. show your work

*asked on November 23, 2015* -
## CALC

An open box is to be constructed so that the length of the base is 4 times larger than the width of the base. If the cost to construct the base is 5 dollars per square foot and the cost to construct the four sides is 3 dollars per square foot, determine

*asked on April 8, 2011* -
## Physics

an artist designs a mobile of light horizontal rods connected by vertical strings and supporting various shaped weights. Find the magnitudes w2, w3, and w4 if w1= 1.00 unit of weight. The numerical values given in the figure all have units of length.

*asked on May 2, 2016* -
## Math help 1 question!!!!!!!!

14. Which statement is true? A. Every rational number is a square root. B. Every irrational number is a fraction. C. Every rational number can be written as a fraction. D. Every square root can be written as a whole number.

*asked on October 10, 2014* -
## Chemistry

H2 + F2--> 2HF deltaH = 518.0 kJ H2 ----> 2H deltaH = 436.8 kJ F2 ---> 2F deltaH = 158.2 kJ (a) calculate Delta H for H + F---> HF (b) what is the standard enthalpy change of formation of F2 Help please!!! i think this is easier than i'm making it. for (b)

*asked on April 28, 2011* -
## American Government

12. Read this excerpt from the U.S Constitution. To declare War, grant Letters of Marque and Reprisal, and make Rules concerning Captures on Land and Water; To raise and support Armies, but no Appropriation of Money to that Use shall be for a longer Term

*asked on September 21, 2016* -
## Chemistry

Light from three different lasers (A, B, and C), each with a different wavelength, was shined onto the same metal surface. Laser A produced no photoelectrons. Lasers C and B both produced photoelectrons, but the photoelectrons produced by laser C had a

*asked on March 6, 2015* -
## chemistry

why do we use the limiting reactant data to calculate delta h? why might it be important to know delta h prior to running a reaction?

*asked on November 13, 2014* -
## Science

Trini adds 10g of baking soda to 100g of vinegar. The mixture begins to bubble. When the bubbling stops, trini finds the mass of the resulting mixture. She determines its mass is 105g. Why has the mass changed? A. A gas has formed and left the mixture B.

*asked on October 20, 2013* -
## 2nd grade Math

Guess my rule with 2 rules. Rule 1:White Diamond,White Square, White Trapezoid Rule 2: Grey Pentagon,Grey Oval, Grey Triangle Fits both rules: Grey Rhombus, Grey Rectangle 1. Guess Rule A: Has 4 sides and 4 corners 2. Guess Rule B: ?? 3. What shape fits

*asked on January 21, 2009* -
## Algebra

Rachel and Lindsay are in third place in a race. Due to a time penalty, they must start the next leg 90 minutes after the second place team. If rachel and lindsay travel at an average rate of 16.8 mph and the second place team travels at an average rate of

*asked on February 8, 2012* -
## Geometry

8. The lateral area of a cone is 555πcm^2. The radius is 15.1 cm. What is the slant height to the nearest tenth of a centimeter? A. 36.8 cm B. 11.7 cm C. 83.8 cm*** D. 25.5 cm 10. What is the volume of the given prism? Round the answer to the nearest

*asked on December 18, 2017* -
## Mathematics

A farmer keeps hens and rabbits on his farm. One day, he counted a total of 70 heads and 196 legs. How many more hens than rabbit does he have? Explain your working please. Your help is greatly appreciated.

*asked on January 15, 2012* -
## Chemistry

Write the equation for the reaction associated with the Ka2 of sulfuric acid, H2SO4. Write the equation for the reaction associated with the Kb2 of carbonate, CO32–.

*asked on January 27, 2013* -
## Algebra

A confectioner sells two types of nut mixtures. The standard-mixture package contains 100 g of cashews and 200 g of peanuts and sells for $1.85. The deluxe-mixture package contains 150 g of cashews and 50 g of peanuts and sells for $2.45. The confectioner

*asked on November 30, 2014* -
## Chemistry

Determine the number of grams of water which are required to dissolve a mixture of 25 g of KNO3 and 2.0 g of CuSo4 * 5H20 AT 100 Degrees celscius?

*asked on February 9, 2011* -
## Math

A conveyor belt carries supplies from the first floor to the second floor which is 30ft higher. The belt makes a 60 degree angle with the ground. How far do the supplies travel from one end of the conveyor belt to the other to the nearest foot? If the belt

*asked on May 25, 2018* -
## Chemistry

Which of the following statements is incorrect concerning the thermochemical equation below? 2SO3(g) 2SO2(g) + O2(g); H° = 198 kJ a. The enthalpy of the reactants exceeds that of the products. b. The reaction is endothermic. c. For the reaction

*asked on July 2, 2013* -
## chemistry

The pH of a 0.55-M aqueous solution of hypobromous acid, HBrO, at 25°C is 4.48. What is the value of Ka for HBrO? how do you solve for Ka?

*asked on November 23, 2010* -
## Chemistry

Calculate the change in enthalpy when 52.0 g of solid chromium at 25°C and 1 atm pressure is oxidized. (H°f for Cr2O3(s) is –1135 kJ/mol.) 4Cr(s) + 3O2(g) 2Cr2O3(s) a. –1135 kJ b. –284 kJ c. –568 kJ d. +1135 kJ e. +568 kJ

*asked on July 1, 2013*