Wednesday
July 23, 2014

Posts by liz


Total # Posts: 1,110

Chemistry
I think that the question is saying why you do subtraction in the equation Qrxn=-Qcal-Qsoln

Chemistry
Why would you subtract the heat capacity of the calorimeter when calculating the heat of the reaction?

Chemistry
For the equation q=cΔt, q=100KJ, initial temp=20 degrees celsius, final temp=31.4 degrees celsius and I need to find c. Do I need to convert the q value from KJ to J?

physics
Fill in blank without a word bank (unit is wave nature of light) 1. As water waves travels through a slit barrier, they bend and spread out. This is known as ______ 2. Two identical waves will interfere destructively, cancelling one another out, when one lags behind the other ...

Chemistry
For an enthalpy lab, why would calculated value differ from the theoretical value (in percent error) for the heat reaction of Mg/HCl and MgO/HCl

SOLVED
I figured out this question

Chemistry
Find the enthalpy of combustion of magnesium using Hess' law given the following data (assume that exactly 100.0 mL of HCl was used in each trial and that HCl is in excess) Magnesium/HCl reaction: Grams of Mg= 0.244g Initial temp= 32.2 degrees celsius Final temp= 21.3 degr...

Chemistry
No, the question only says Mg

Chemistry
why can't the enthalpy of magnesium be measured using a coffee cup calorimeter?

chemistry
It is ok to have a negative percent error? I got a negative value for the percent error of the enthalpy of the formation of methane gas

Chemistry
The combustion reaction of Mg +1/2 O2-->MgO produces a very bright white flame and high heat. Verify that the following reactions produce the same overall reaction: a) MgO+2HCl-->MgCl2+H2O b) Mg+2HCl-->MgCl2+H2 c) H2+1/2O2-->H2O ΔH°= -285.8 KJ/mol

Chemistry
I am to use this formula to find ΔH°f,methane: ΔH°comb=2ΔH°f,water+ΔH°f, carbon dioxide-ΔH°f,methane-2ΔH°f,oxygen For ΔH°comb, the value is 884 KJ/mol For ΔH°f,water, the value is -285.8 For ΔH°f,...

Chemistry
ok I got it now!

Chemistry
Ok thanks! I used PV=nRT to calculate the mols but I got a larger number. Here's what I did: P= 1.000 atm V= 0.271 L R= 0.08206 Latm/molK T= 2.3 K and I got 1.436 as my answer

Chemistry
A calorimeter is filled with 10.0 millimole (mmole) of methane gas and an excess of oxygen. When burned, the ignition wire releases 140.77 J of heat. The heat capacity of the calorimeter is 4.319 KJ°C-1. qwire= 140.77 J Calculate ΔHcomb. Recall that ideal gas law is P...

Chemistry
Ok I understand it now! Thank you so much!

Chemistry
Oh so answer would be 907 J/mol? also for the thermochemical equation you said it would be CH4 + 2O2 ==> CO2 + 2H2O with ΔH=- 890 kJ/mol but I don't know how to calculate that value

Chemistry
I have previously posted this question, but now I am lost question: A calorimeter is filled with 10.0 millimole (mmole) of methane gas and an excess of oxygen. When burned, the ignition wire releases 107.2 J of heat. The heat capacity of the calorimeter (including the bomb and...

Chemistry
I got 0.907 KJ for ΔHcomb but I don't know if its correct. I also don't know how to write the equation. -------- question: A calorimeter is filled with 10.0 mole of methane gas and an excess of oxygen. When burned, the ignition wire releases 107.2 J of heat. The h...

Chemistry
Yes the initial temperature is 24.75 degrees celsius and the final temperature is 26.85 degrees celsius

Chemistry
I got 0.907 KJ for ΔHcomb but I don't know if its correct. I also don't know how to write the equation. -------- question: A calorimeter is filled with 10.0 mole of methane gas and an excess of oxygen. When burned, the ignition wire releases 107.2 J of heat. The h...

Unified field theory
Einstein sought to discover a unified field theory that would explain the behaviour of all fields. What evidence have you seen to suggest that such a theory exists? Is there anything to suggest that it doesn't?

physics
A particle with a charge of -4.0x10^-5 C, a mass of 2.0x10^-7 kg and a velocity of 6.0x10^4 m/s [W] is travelling perpendicularly through an external magnetic field such that the force of gravity is balanced by the magnetic force. Determine the direction and magnitude of the e...

physics
A charge with a value of 3.0 x 10^-5 C is located 3.0 cm from a charge with a value of 6.0 x 10^-5 C. Determine the distance from the larger charge to the point where the total electric field is zero

chemistry
How would polyethylene have the VSEPR shape of tetrahedral?

physics
A particle with a charge of -4.0x10^-5 C, a mass of 2.0x10^-7 kg and a velocity of 6.0x10^4 m/s [W] is travelling perpendicularly through an external magnetic field such that the force of gravity is balanced by the magnetic force. Determine the direction and magnitude of the e...

Physics help
A charge with a value of 3.0 x 10^-5 C is located 3.0 cm from a charge with a value of 6.0 x 10^-5 C. Determine the distance from the larger charge to the point where the total electric field is zero

Physics help
A particle with a charge of -4.0x10^-5 C, a mass of 2.0x10^-7 kg and a velocity of 6.0x10^4 m/s [W] is travelling perpendicularly through an external magnetic field such that the force of gravity is balanced by the magnetic force. Determine the direction and magnitude of the e...

physics
A charge with a value of 3.0 x 10^-5 C is located 3.0 cm from a charge with a value of 6.0 x 10^-5 C. Determine the distance from the larger charge to the point where the total electric field is zero

physics
A particle with a charge of -4.0x10^-5 C, a mass of 2.0x10^-7 kg and a velocity of 6.0x10^4 m/s [W] is travelling perpendicularly through an external magnetic field such that the force of gravity is balanced by the magnetic force. Determine the direction and magnitude of the e...

physics
A 1000 kg rocket without an internal propulsion system is launched with an initial speed of 7.00 x 10^2 m/s. Determine the maximum height attained by the rocket

physics
1. which of the following is not true about magnetic field lines a) mag. field lines flow from North to South inside the magnet b) mag. field lines do not cross c) mag. field line density is proportional to field strength d) mag. field is strongest closest to the ends of a bar...

physics
Would the answer be c? The electrical potential 10 cm from an electron is: a) 1.4x10^-8 V b) 1.4x10^-10 V c) 1.4x10^-7 V d) 1.2x10^-4 V

physics
Would the answer be a? Which two forces balanced in the Millikan oil drop experiment a) electric and gravitational b) electric and magnetic c) magnetic and gravitational d) none of the above

physics
thanks! and thanks for the link, its quite useful!

physics
The escape velocity on the moon is: a) 5.64x10^6 m/s b) 1.68x10^3 c) 160 m/s d) 2.38x10^3 m/s

physics
thanks!

physics
If the electric field near a proton is 9.00 x 10^-3 N/C, what is the distance from the proton?

chemistry
explain whether using solid sodium hydroxide pellets rather than aqueous sodium hydroxide would alter the enthalpy

chemistry
Why would you have to subtract the heat capacity of the calorimeter when calculating the heat of the reaction?

chemistry
Why would you have to subtract the heat capacity of the calorimeter when calculating the heat of the reaction?

Physics
all electric field lines start on positive charges. explain why this makes sense.

physics
What is a charge dipole a basic model of? would it be a magnet?

Physics- help please
A beta particle (fast moving electron) is released by a nuclear decay and starts travelling at 1.5x10^6 m/s [NΘE] in the Earth's magnetic field which has a value of 3.0x10^-5 T. If the force experienced by the beta particle is 4.34x10^-18 N, determine the angle betwee...

Physics
Two parallel wires are carrying current. If the currents are in the same direction, what is the interaction between the two wires and why? How would this be different in the currents were in opposite directions?

Physics help
1. if the magnetic field is 2.1 m from a current carrying wire is 7.1x10^-5 T, what is the current flowing through the wire? 2. The electromagnet in an MRI has a magnetic field of 2.5 T. If there are 100 A of current running through the magnet, how many turns are there in a 1....

Physics
1. You are looking into a current carrying solenoid and notice that the compass needle indicates that you are at the south end of the magnetic field. What is the direction of the current in the coil and how do you know? Would it be clockwise because current moves towards the s...

Physics- check answer please
1. A 15 kg boy falls out of his bed at a height of 0.50 m. What is the amount of gravitational potential energy lost by the boy? my answer: 74 J 2. What is the speed of a 0.25 kg ball if its kinetic energy is 15 J? my answer: 11 m/s 3. if the speed of an object is tripled and ...

Physics
a child throws a ball in a net where it gets stuck. Does the motion of this ball defy the law of conservation of momentum? explain

physics word problem
A 60.0 kg girl stands up on a stationary floating raft and decides to go into shore. She dives off the 180 kg floating raft with a velocity of 4.0 m/s [W]. Ignore the substantial friction real objects in water experience. What is the speed of the raft just after the girl dives?

physics
How would I answer number 3? 1. A sumo wrestler originally jumps 10 cm above a trampoline but has the same total energy of a small ball that was 200 cm higher than the trampoline. What causes this equivalency? 2. If a 40 kg gymnast and a 400 kg sumo wrestler each dropped from ...

Physics
A sumo wrestler originally jumps 10 cm above a trampoline but has the same total energy of a small ball that was 200 cm higher than the trampoline. What causes this equivalency?

Physics -- check answers please
Use g=10 N/kg in this assignment. 1. What is the gravitational energy (relative to the unstretched surface of the trampoline) of the 20 kg ball at its apex 2 m above the trampoline? I got 400 J 2. What is the kinetic energy of the ball just before impacting the trampoline? I g...

Check answers please?
Use g=10 N/kg in this assignment. 1. What is the gravitational energy (relative to the unstretched surface of the trampoline) of the 20 kg ball at its apex 2 m above the trampoline? I got 400 J 2. What is the kinetic energy of the ball just before impacting the trampoline? I g...

Physics
fill in the blank ( Energy and momentum unit) 1. the work done to stretch a spring is not equal to the to force multiplied by displacement because force is ____ as the spring stretches 2. A child goes down a slide at the playground, gaining speed as she goes. Her momentum ____...

Physics- check answer please
I am supposed to fill in the blanks without a word bank. 1. I you push a crate with 40 N of force at an angle of 30 degrees and your friend pushes with a force of 40 N horizontally, the amount of work you are doing is _____ the amount of work your friend is doing on the crate ...

Physics
Which of the following is an inertial frame of reference? a) a child on a moving swing observes the child next to them moving in sync b) a child on a moving swing observes a ball that they throw to their parents standing on the ground c) a child observes the motion of the plan...

physics
1. what happens to the force required for an object to maintain circular motion if the period is halved (goes twice as fast around the circle)? a) force doubles b) force quadruples c) force is halved d) force is quartered 2. In a pulley problem involving an inclined plane: a) ...

physics
1. the applied force on a stationary object is less than the maximum force of static friction. Which of the statements are false a) the object will move backwards b) the actual force of static friction will be equal to the applied force c) the object will remain stationary unt...

Physics
In projectile motion, how would you find the final velocity of the object just before it hits the ground a) find the second vertical velocity b) add the final and horizontal velocities directly c)add the final and horizontal velocities as vectors d) add the final and horizonta...

Physics help
how might life be different if static friction did not exist? give three examples and reference formulas to support your answers I have three examples but I do not understand what the questions mean by reference formulas

Physics multiple choice
1. What happens to the force required for an object to maintain circular motion if the period is halved (goes around twice as fast around the circle)? a) force doubles b) force quadruples c) force is halved d) force is quartered my answer: c 2. Which is true a) the acceleratio...

Physics
1. A ball is launched from a cliff with an initial velcity of 10 m/s at an angle of 40 degrees above horizontal. If the ball lands 24 m away, determine the height of the cliff. 2. if the mass A is 1 kg and the mass of B is 6.0 kg, determine the acceleration of the system and t...

Physics
how might life be different if static friction did not exist? give three examples and reference formulas to support your answers I have three examples but I do not understand what the questions mean by reference formulas

Physics
I got 25 m/s for #2 but I still do not know how to answer #1 and #3

Physics
1. A ball is launched from a cliff with an initial velcity of 10 m/s at an angle of 40 degrees above horizontal. If the ball lands 24 m away, determine the height of the cliff. 2. if the mass A is 1 kg and the mass of B is 6.0 kg, determine the acceleration of the system and t...

Physics
1. What happens to the force required for an object to maintain circular motion if the period is halved (goes around twice as fast around the circle)? a) force doubles b) force quadruples c) force is halved d) force is quartered my answer: c 2. Which is true a) the acceleratio...

math word problems
A room is a square with integer dimensions. it is made 3 feet wider and 2 feet deeper. the increase in area is 46 square feed. What were the dimensions of the old room?

chemistry
What is the monomer and polymer structure of DNA?

Calculus
Consider the function f (x) = 2x^3 - 3x^2 - 72x + 7 Find and classify the critical points. Identify the intervals of increase and decrease, and state the intervals of concavity.

Physics
what is the role of a commutator in a DC motor?

Physics -- check answers please
The earth's magnetic field a) is slightly off centre compared to the Earth's rotational axis of rotation b) has its magnetic south pole at the geographic north pole c) attracts the north end of the compass needle to the geographic north pole d) all of the above Would i...

Physics
The earth's magnetic field a) is slightly off centre compared to the Earth's rotational axis of rotation b) has its magnetic south pole at the geographic north pole c) attracts the north end of the compass needle to the geographic north pole d) all of the above 2. A ma...

Calculus Reply
The only info I have is when the container is half full which is 500mL in 32.7 seconds and quarter full is 250mL in 23.8 seconds.

Calculus
I did an experiment where I had to measure how fast water flowed out of a container at different times and with different volumes (from 0mL-1000mL in increments of 50). I also had to record the values into a table and graph them. (I got an exponential function). I got a slope ...

Calculus
Thanks! It is an exponential graph

Calculus
I have a data table and I graphed the data. I have to find the slope of a tangent at t=0. Would the slope just be zero?

Calculus
I did an experiment where I had to measure how fast water flowed out of a container at different times and with different volumes. I also had to record the values into a table and graph them. (I got an exponential function). I am to answer the following questions and I do not ...

Calculus- answer check
A brand new stock is also called an initial public offering. This model predicts the percent overvaluation of a stock as R(t)=9t((t-3)^3/2.718) where is the overvaluation in percent and t is the time in months after the initial issue. Use the information provided by the first ...

derivative
Would the first derivative of R(t)=9t[(t-4)^3/2.718] be R'(t)=3.311258278(3(t-4)^2(t)+(t-4)^3) and the second derivative be R''(t)=3.311258278(6(t-4)x+6(t-4)^2)?

average and instantaneous rate of change
what is the difference between an average rate of water flow and an instantaneous rate of water flow?

Calculus
Sorry about that. It looks like thins: R(t)= 9t[(t-4)^3/2.718] The 9t is on the outside without a denominator

Calculus
A brand new stock is also called an initial public offering. In this model, the period immediately after the stock is issued offers excess returns on the stock—that is, the stock is selling for more than it is really worth. One such model predicts the percent overvaluatio...

Calculus
thanks! Would the first derivative be R'(t)=3.311258278(3(t-4)^2(t)+(t-4)^3) and the second derivative be R''(t)=3.311258278(6(t-4)x+6(t-4)^2)

Calculus
A brand new stock is also called an initial public offering. In this model, the period immediately after the stock is issued offers excess returns on the stock—that is, the stock is selling for more than it is really worth. One such model predicts the percent overvaluatio...

Calculus
determine f" if f(x)=sqrt(x^3+2)

Calculus
If f(x1)>f(x2) for every x1>x2 then what is the behaviour of f(x)?

Calculus
If f(x1)>f(x2) for every x1>x2, then what is the behaviour of f(x)? I believe that the answer is that f(x) is increasing but I do not know how to show my work for that

Calculus
I figured out the answer!

Calculus
A movie theater wants to determine the price per ticket that should be charged in order to maximize its revenue. The theater can accommodate 2000 movie goers per night, but the average attendance is about 1400 people per night. The average ticket price is about $8.00. Market r...

physics- answers check
5. A magnetic field map shows a. the direction of the magnetic field. b. a few representational field lines. c. relative strength of the magnetic field. d. All of these choices are correct. my answer: d 6. Magnetic field lines a. can cross each other when the field is strong. ...

physics- answers check
1. For a bar magnet, the magnetic field lines point a. towards the South pole. b. towards the North pole. c. always towards the magnet. d. always away from the magnet. my answer: a 2. Magnetic field lines a. are straight lines. b. are always circles. c. form continuous loops. ...

Physics
1. A 40Ω , 20Ω and 60Ω resistor is connected in a parallel circuit. Which resistor would have the greatest current passing through it and why? 2. A 24Ω , 8Ω and 60Ω resistor is connected in a series circuit. Which resistor would have the greatest ...

Physics question
Does the crest of a wave usually have a larger amplitude than the trough?

Physics
A vibrating point on a spring travels 60 mm during three cycles. What is the amplitude of the vibration?

Physics- check answer please
1. A vibrating point on a spring travels 60 mm during three cycles. What is the amplitude of the vibration? a) 0.05 mm b) 5.0 mm c) 15.mm d) 20.mm e) 180 mm my answer: I got 10 mm but it is not listed as an option

Physics
When a tuning fork of unknown frequency is sounded simultaneously with a 512 Hz tuning fork, 20 beats are heard in 4.0 seconds. What are the possible frequencies of the unknown tuning fork?

Physics waves
1. A vibrating point on a spring travels 60 mm during three cycles. What is the amplitude of the vibration? a) 0.05 mm b) 5.0 mm c) 15.mm d) 20.mm e) 180 mm my answer: I got 10 mm but it is not listed as an option 2. When a tuning fork of unknown frequency is sounded simultane...

Physics waves
1. A vibrating point on a spring travels 60 mm during three cycles. What is the amplitude of the vibration? a) 0.05 mm b) 5.0 mm c) 15.mm d) 20.mm e) 180 mm my answer: I got 10 mm but it is not listed as an option 2. When a tuning fork of unknown frequency is sounded simultane...

Physics waves- check answers please
1. A vibrating point on a spring travels 60 mm during three cycles. What is the amplitude of the vibration? my answer: I got 10 mm but I'm not sure if it is the correct answer. 2. For two connect pendulums to resonate, they must have the same: a) mass b) amplitude c) densi...

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