osmotic pressure chemistry

64,562 results, page 46
  1. chem

    You have two flasks of equal volume. Flask A contains H2 at 0°C and 1 atm pressure. Flask B contains CO2 gas at 0°C and 2 atm pressure. Compare these two gases with respect to each of the following mass of gas (Flask A:Flask B)
  2. physics

    Gas is confined in a tank at a pressure of 10 atm and a temperature of 14◦C. If 58 percent of the gas is withdrawn and the temperature is raised to 50◦C, what is the new pressure in the tank?
  3. science

    At a pressure 43 kPa, the gas in a cylinder has a volume of 11 liters. Assuming temperature remains the same, if the volume of the gas is decreased to 5 liters, what is the new pressure? kPa Im guessing it 58 or 77x10^3
  4. Physics

    A tire contains air at a pressure of 2 bar at 15 degrees Celsius. If the tires volume is unchanged, what will the air pressure in it be when the tire warms up to 40 degrees Celsius as the car is driven?
  5. vaporization lab

    A graduated cylinder containing some air is immersed in water. The height between the the water surface and the top of the water inside the graduated cylinder is 106mm. Calculate the correction that must be added to the barometric pressure to find the
  6. Chemistry

    The vapor pressure of pure water at 90celsius is normally 525.8 but decreased 483mmHg upon addition of an unknown amount of KNO3 to 286.9g H2O at this temperature. how many grams KNO3 were added. ASSUME COMPLETE DISSOCIATION OF SOLUTE. Tried all solutions
  7. Chemistry

    The running engine of an automobile produces carbon monoxide (CO), a toxic gas, at the rate of about .102mol CO per minute. a car is left idiling in a poorly ventilated garage that is 60m long, 4 m wide, and 2.2 m high at 20 degrees C. what will the
  8. Chemistry

    You have a reaction using the following criteria: 1.3456 g of barium chloride solution (0.786M) is mixed with 1.20089 g of sodium sulfate solution (1.3M). The ambient pressure is 754.564 mmHg and the temperature is 56.889 degrees celsius. Determine the
  9. Chemistry

    N2(g) + O2(g) → N2O5(g) What volume of oxygen gas reacts to yield 750.0 cm3 of N2O5? The reaction conditions are 350°C and 2.50 atm pressure. 2N2 + 5 O2 = 2N2O5 I balanced correctly. What is my next step to solve this problem. I am confused and I
  10. Chemistry

    A 500 mL metal cylinder holding 0.100 moles of helium gas is known to rupture at a pressure of 10 atmospheres. At what temperature, in °C, will the container fail? Here is what I came up with: T= (1.00mol x 0.0821 LxATM/KxMOL) / 10atm x 0.5L =0.01642K
  11. Chemistry

    Compute the volume of helium at 1.0 atm and 298 K that will be collected if 2.5 g of 222Rn is stored in a container able to expand to maintain a constant pressure for 15 days. Assume that 222Rn decays to 218Po with a half-life of 3.824 days.
  12. chemistry

    The following equation represents the partial combustion of methane, CH4. 2CH4(g) + 3O2(g) > 2CO(g) + 4H2O(g) At constant temperature and pressure, what is the maximum volume of carbon monoxide that can be obtained from 3.39 x 102 L of methane and 1.70
  13. Chemistry

    All volume measurements are carried out at the same temperature and pressure. If 20.0 L of O2 (g) are allowed to completely react with a sample of pure CH4 (g) in a combustion process producing CO2 (g) as the only carbon-containing product, what is the
  14. Chemistry

    One mole of N2 and three moles of H2 are placed in a flask at 375 C. Calculate the total pressure of the system at equilibrium if the mole fraction of NH3 is 0.21. The Kp for the reaction is 4.31*10^4. I assume this to be the reaction N2 + 3H2 --> 2NH3
  15. chemistry

    (L2bar/mol2) (L/mol) Acetylene 4.448 0.05136 Calculate the difference in pressure (in atm) when 100.0g of acetylene acts as an ideal gas versus as a real gas in a 100L tank at a temperature of 1000K.
  16. Chemistry

    One mole of N2 and three moles of H2 are placed in a flask at 375 C. Calculate the total pressure of the system at equilibrium if the mole fraction of NH3 is 0.21. The Kp for the reaction is 4.31*10^4. I assume this to be the reaction N2 + 3H2 --> 2NH3
  17. chemistry

    describe how the changes would affect each of the following chemical equilibra involving gases.. 2NO2(arows facing both direction) N204+HEAT 1.THE TEMPERATURE IS INCREASE 2.THE PRESSURE IS DECREASED 3.THE CONCENTRATION OF NO2 is increase 4.THE
  18. Physics

    On a cool morning, when the temperature is 13 C, you measure the pressure in your car tires to be 30 psi. After driving 50 mi on the freeway, the temperature of your tires is 42C. What pressure will your tire gauge now show? T1 = 13 C T2 = 42 C P1 = 30 psi
  19. Jennifer

    I asked this question yesterday and it was answered, but I still have a question on it. Standard entropies for substances are defined at a pressure of exactly 1 bar in some books or exactly 1 atm(760 torr) in different books. For gases, this correction
  20. physics

    Many cultures around the world still use a simple weapon called a blowgun, a tube with a dart that fits tightly inside. A sharp breath into the end of the tube launches the dart. When exhaling forcefully, a healthy person can supply air at a gauge pressure
  21. Chemistry

    Suppose that 2.3 L of gas at 35°C and 1.0 atm is expanded to 4.5 L at 42°C. What will the final pressure of the gas be? (Ti in Kelvins=308.15; Tf(K)=315.15) Can someone please show me how to plug the values into the Combined Gas Law formula to calculate
  22. science

    Calculate the volume of solution that has a vapour pressure of 25.8 mbar and contains 200.3 g of galactose, C6H12O6, at a temperature of 22.0 °C. The vapour pressure of pure water at 22 °C is 26.40 mbar, the density of water is 1.00 g mL-1, and assume no
  23. chemistry

    If you place 10.0 L of propanol (C3H8O) in a sealed room that is 3 m long, 2.75 m wide, and 2.5 m high, will all the propanol evaporate? If some liquid remains, how much will there be? The vapor pressure of propanol is 10.7 torr at 25 °C, and the density
  24. Chemistry

    A balloon is floating around outside your window. The temperature outside is 39 degree celsius, and the air pressure is 0.800atm . Your neighbor, who released the balloon, tells you that he filled it with 3.10 moles of gas. What is the volume of gas inside
  25. Health

    1). Which three kinds of direct pressure do you experience most often? A: Persuasion, explanations, and put-downs are the three kinds of direct pressure I experience most often. 2). Which three kinds of indirect pressure do you experience most often? A:
  26. science help

    The two tables below give the relative-risk of developing a stroke, in relation to blood pressure and body mass index. The data are based on a population of men from the USA. The values in the first table are given in comparison with the total population.
  27. thermodynamic

    an engine operates on the carnot cycle between the temperature limits of 250c and 50c. the pressure and the volume at the start of the isothermal expansion are 6 bar and 0.1 m^3 respectively. pressure after isothermal expansion is 3 bar. assume
  28. Maths *have answer, want method* Urgent!

    Suppose that the blood pressure of the human inhabitants of a certain Pacific island is distributed with mean, \mu = 108 mmHg and standard deviation , \sigma = 6 mmHg. According to Chebyshev's Theorem, at least what percentage of the islanders have blood
  29. dr. bob

    Use the data in Table 5.4 to calculate the partial pressure of He in dry air assuming that the total pressure is 1.0 atm. Assuming a temperature of 21°C, calculate the number of He atoms per cubic centimeter. atoms/cm3 .00000524 - atmospheric composition
  30. chem

    a sealed cylinder of a gas contains nitrogen gas at 1.00*10^3 kPa pressure and a temperature of 20C. They cylinder is left in the sun and the temperature of the gas increases to 50C. What is the new pressure in the cylinder?
  31. physics

    I recently did an experiment where I measured pressure at a few heights. The question I cam having trouble with is how to find the density of the air between the top and bottom. The difference in pressure from the top to bottom is 52.6 torr (692.5 to
  32. Math Physics

    Find the water pressure at ground level to supply water to the third floor of a building 8.00 m high with a pressure of 325 kPa at the third level So the given is h=8.00 Ptop=325kPa Density water = 1000 Would I need to set it up like 325+1000*9.81*8.00
  33. Fluid Mechanics

    Find the water pressure at ground level to supply water to the third floor of a building 8.00 m high with a pressure of 325 kPa at the third level So the given is h=8.00 Ptop=325kPa Density water = 1000 Would I need to set it up like 325+1000*9.81*8.00
  34. physics

    A closed container with a volume of 8000cm^3 is filled with Xenon gas. the temperature is 273K and the pressure is 2 atm. How many moles of Xenon are in the container? The container is now submerged in boiling water until the gas inside the container is at
  35. Physics

    Explain Why the pressure of a gas in a nitrogen container falls continuously when the gas is continuously taken away while the pressure of a gas in a chlorine container remains constant until nearly all the gas is withdrawn
  36. Calculus

    the drop in blood pressure of a typical patient who is given a certain medication is given by F(x)=0.028x^2(19-x) where x is the amount of medication in cubic centimeters. What is the maximum drop in blood pressure for this patient?
  37. Chem

    Knowing what information would allow you to order gas molecules according to their velocity? A. Pressure and temperature B. Volume and molecular mass C. Pressure and volume D. Temperature and molecular mass
  38. chem

    Knowing what information would allow you to order gas molecules according to their velocity? A. Pressure and temperature B. Volume and molecular mass C. Pressure and volume D. Temperature and molecular mass
  39. physics

    An automobile tire has a pressure of 325 kPa when the temperature is 10 degrees Celsius. If the temperature of the tire rises to 50 degrees Celsius and its volume is constant,what is the new pressure?
  40. Physics

    A compartment measures 3.5 meters by 5.5 meters and is 3 meters high. A fire raises the temperature from 68 degrees F to 1500 degrees F. If the starting pressure was 1 atmosphere, what volume is present at the elevated temperature assuming the compartment
  41. Physics (Please help!!!)

    1) If a 10. m3 volume of air (acting as an ideal gas) is at a pressure of 760 mm and a temperature of 27 degrees Celsius is taken to a high altitude where the pressure is 400. mm Hg and a temperature of -23 degrees Celsius, what volume will it occupy?
  42. physics

    If a person weighs 160 pounds, and the surface area of the bottom of both feet combined is 200 cm2. What is the pressure under the person’s feet (unit: N/m2)? What is the pressure if the person stands on only one foot (unit: N/m2)? [Hint: 1 kg = 2.2 lbs,
  43. Physics

    I understand there is a relationship between pressure & temperature in a sealed rigid container. An open container is placed in a freezer at -15 degrees C then the door is opened and the cap replaced with the freezer at 1000mb what will the pressure be
  44. Physic

    Water enters a horizontal pipe with a rectangular cross section at a speed of 1.00 m/s. The width of the pipe remains constant but the height decreases. 27.3 m from the entrance, the height is half of what it is at the entrance. If the water pressure at
  45. chem

    N2H4 is decomposed in a closed container according to this reaction: N2H4 → N2 + 2H2 . If the temperature is constant and the initial pressure of N2H4 is 800mm, what will the pressure in millimeters be after the decomposition to N2 + 2H2? Im having
  46. physics

    Water enters a horizontal pipe with a rectangular cross section at a speed of 1.00 m/s. The width of the pipe remains constant but the height decreases. 27.3 m from the entrance, the height is half of what it is at the entrance. If the water pressure at
  47. chemistry

    1. the volume of an idea gas is 2.06L at standard temperature and pressure. Calculate the volume at 1.75 atm and 27CELCIUS. 2. Ethane, C2h6 has a molar heat of vaporization of 15kj/mole. How many kilojoules or energy are required to vaporize 5 g of ethane?
  48. Chemistry

    How many liters of Carbon Dioxide are formed by burning 6011.0 grams of C3H7OH with excess of oxygen gas and is carried out at 20.00 degrees Celsius, and 1.150 atm of pressure. I know this needs PV=nRT but the burning and excess part is throwing me off.
  49. Chemistry

    I live in an area of 1014 millibars barometric pressure and I have an imaginary balloon with 22 grams of CO2 and a temperature of 61 degrees Fahreheit. What is the volume of the gas in liters. I know to use the Ideal gas law but how do I convert millibars
  50. chemistry

    What is the pressure in millimeters of mercury of 0.0115mol of helium gas with a volume of 211ml at a temperature of 25 degrees celsius? Ok so I've come up with many different answers but none are right. You convert the mL to L and the temperature to
  51. Chemistry

    At 298K and 1bar pressure, the density of water is 1.00 g/cm^3 , Cpm = and 75.3 J/Kmol. The change in volume with temperature is given by delta V = ViB(deltaT), where B, the coefficient of thermal expansion, is 2.07 * 10^-4 K^-1. If the temperature of 350g
  52. college chem

    A balloon is filled with 2.3 cm3 helium gas at 112.1 atm pressure. What will be the new pressure (atm) if the volume is changed to 44.7 cm3? P1V1=P2V2 (112.1)(.0023)=(P2)(.0447) the answer i got was 54.85 so would the answer be 54.85 atm?
  53. Physics

    An ideal gas at 6.0°C and a pressure of 1.92 105 Pa occupies a volume of 2.10 m3. (a) How many moles of gas are present? moles (b) If the volume is raised to 4.60 m3 and temperature raised to 30.5°C, what will be the pressure of the gas? Pa I used the
  54. phycis

    A cylindrical tank has a tight-fitting piston that allows the volume of the tank to change. The tank contains 0.5m^3 of air at a pressure of 2*10^5 Pa. The piston is slowly pushed in until the pressure of the air is increased to 2.5*10^5 Pa. If the
  55. physics

    Water is flowing through a horizontal pipe of varying cross section. At section 1,the diameter is 12cm at a pressure of 80000 Pa. At section 2, the pipe has a diameter of 6cm and the pressure is 60000 Pa. Find the speed of water through sections 1 and 2.
  56. physics

    A sample of monatomic gas (£^ = 5/3) is expanded adiabatically from an initial temperature, volume, and pressure of 230. ¢XC, 6.00 litres, and 5.00 kPa, respectively, to a final volume of 7.00 litres. (a) What is the final pressure of the gas? (b) How
  57. Physics

    A 5.0x10^-3 m^3 container holds 4.90 g gas when the pressure is 75.0 cm Hg and the temperature is 50.0 degrees C. What will be the pressure if 6.00 g of this gas is confined to a 2.0x10^-3 m^3 container at 0.0 degrees C? Do I simply need to use the
  58. physics

    An ideal gas at 19.8 °C and a pressure of 2.79 x 105 Pa occupies a volume of 3.66 m3. (a) How many moles of gas are present? (b) If the volume is raised to 7.20 m3 and the temperature raised to 28.5 °C, what will be the pressure of the gas? I got a)
  59. physics

    Water flows steadily along a uniform flow tube of cross-section 30cm^2. The static pressure is 1.20 x 10^5 Pa and the total pressure is 1.28 x 10^5 Pa. Calculate the flow velocity and the mass of water per second flowing past a section of the tube.
  60. physic

    mars once may have had an ocean 0.50 km deep. the acceleration due to gravity on mars is 0.379g, and we shall assume (unrealistically) the consisted of fresh water. a)what would be the guage pressure(in Pa)at the bottem of this martian ocean? b)what is the
  61. chemistry

    A balloon is inflaed outdoors on a cold day in lowa at a temperature of -40 c to a volume of 2.00 l. If the pressure remains constant, what is the volume of the same balloon if taken indoors at a temperature of 25 c?
  62. Chemistry

    A sealed flask containing water and N2 gas in equilibrium is at a temperature of 25°C. If the concentration of N2 gas in the solution is 1.4 x 10-3 M, what is the partial pressure of N2 gas in the container? (kH for N2 gas in water is 6.1 x 10-4 M/atm at
  63. Chemistry

    If a balloon containing 1000 L of gas at 50 degrees Celsius and 101.3 kPa rises to an altitude where the pressure is 27.5 kPa and the temperature is 10 degrees Celsius, its volume there is?
  64. Chemistry

    A 3.00- L flask is filled with gaseous ammonia, N H 3 . The gas pressure measured at 28.0 ∘ C is 2.05 atm . Assuming ideal gas behavior, how many grams of ammonia are in the flask?
  65. Chemistry

    What volume will 823 mL of SO3 gas at 11 degrees celsius and 720 mm Hg occupy when the pressure is raised to 1.55atm and the temperature is raised to 81 degrees celsius?
  66. Chemistry

    the gaseous product of a reaction is collected in a 25.0L container at 27c. the pressure in the container is 300.0 kpa and the gas has a mass of 96.0g. what is the molar mass of the gas?
  67. CHEMISTRY

    NEED HELP (Combined gas Law) A gas at a pressure of 1.50 atm has a volume of 200 mL. Calculate the new volume if the pressue changes to 1.20 atm. Assume constant temperature.
  68. Chemistry

    A sample of a gas at STP has its temperature raised to 510C and its pressure raised to 5 atm. If the initial volume of this gas is 100.0 ml, what will the final volume be?
  69. Chemistry

    Hi! I have another question. So 1 kcal of heat is added to 1.5 L of oxygen in a container at constant pressure. (1atm). Then volume increases to 3.1L. they want to know total energy change. Now i think the formula is DH=DU + PDV so what i did was DH = 1
  70. chemistry

    A 7.30-L container holds a mixture of two gases at 45 °C. The partial pressures of gas A and gas B, respectively, are 0.410 atm and 0.620 atm. If 0.150 mol of a third gas is added with no change in volume or temperature, what will the total pressure
  71. Chemistry

    Hi! I have another question. So 1 kcal of heat is added to 1.5 L of oxygen in a container at constant pressure. (1atm). Then volume increases to 3.1L. they want to know total energy change. Now i think the formula is DH=DU + PDV so what i did was DH = 1
  72. Chemistry

    A 8.25-L container holds a mixture of two gases at 39 °C. The partial pressures of gas A and gas B, respectively, are 0.186 atm and 0.884 atm. If 0.120 mol of a third gas is added with no change in volume or temperature, what will the total pressure
  73. Chemistry

    At 25oC, the equilibrium pressure of ammonia vapour above a 0.500 M aqueous ammonia solution is 0.84 kPa. Calculate the Henry's law constant for ammonia in M/bar. Do not include units. Include 4 significant figures.
  74. chemistry

    A 8.90-L container holds a mixture of two gases at 45 C. The partial pressures of gas A and gas B, respectively, are .294 atm and .860 atm. If .100 mol of a third gas is added with no change in volume or temperature, what will the total pressure become?
  75. Chemistry

    at 25C and 795 torr, carbon dioxide has a solubility of 0.0356 M in water. What is the solubility at 25 C and 2070 torr? ____ M I know that at a given temperature, the solubility of a gas in a liquid is directly proportional to its pressure but how would
  76. chemistry

    1.0 mol of nitrogen oxide NO and 1.0 mol of oxygen were mixed in a container and heated to 450 oC. At equilibrium the number of moles of oxygen was found to be 0.70 mol. The total pressure in the vessel was 4.0 atm. Calculate the value of Kp for the
  77. Chemistry

    A 7.30-L container holds a mixture of two gases at 45 °C. The partial pressures of gas A and gas B, respectively, are 0.342 atm and 0.527 atm. If 0.250 mol a third gas is added with no change in volume or temperature, what will the total pressure become?
  78. Chemistry

    Hi! I have another question. So 1 kcal of heat is added to 1.5 L of oxygen in a container at constant pressure. (1atm). Then volume increases to 3.1L. they want to know total energy change. Now i think the formula is DH=DU + PDV so what i did was DH = 1
  79. 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
  80. Chem-E / Chemistry

    Calculate the rate of heat required to bring 1.80mol/hr of HBr gas from 37.0 C to 434.0C at atmospheric pressure (Heat capacity of HBr is described by eq.) Cp (kJ/mol * C) = a + bT + cT^2 + dt^3 T is in C and HBr - a = 2.910x10^-2, b= -2.27x10^-7, c=
  81. chemistry

    A 8.75-L container holds a mixture of two gases at 23 °C. The partial pressures of gas A and gas B, respectively, are 0.317 atm and 0.755 atm. If 0.100 mol of a third gas is added with no change in volume or temperature, what will the total pressure
  82. Chemistry

    A 9.00-L container holds a mixture of two gases at 43 °C. The partial pressures of gas A and gas B, respectively, are 0.257 atm and 0.579 atm. If 0.110 mol a third gas is added with no change in volume or temperature, what will the total pressure become?
  83. Chemistry

    The reaction NO2(g) + NO2(g) → N2O4(g) is second order with a rate constant of 0.044 /M·s at a particular temperature and pressure. If the initial concentration of NO2(g) is 0.100 M, what is the concentration of NO2 after 20 minutes?
  84. Chemistry

    The boiling point of alcohol is 78.3 degrees Celcius at 760 mm atm pressure. Would the boiling point be higher or lower than 78.3 degree Celcius at hugher altirudes? Why?
  85. chemistry

    The volume of 02 collected over water at 25 Celcius and 740 torr was 250 mL. What volume will the dry 0x occupy at STP (Vapor pressure of water at 25 celcuis is 23.8 torr)
  86. Chemistry Honors

    Use the diagram below to answer the following question. What will be water's phase of matter at a temperature of 74°C and a pressure of 4.4 mm? A. mostly liquid B. mostly solid C. solid, liquid, or gas D. mostly gaseous Answer: D
  87. Chemistry

    In a 25.8 liter vessel of nitrogen gas that is heated from 10 degrees Celsius to 110 degrees Celsius to reach a final pressure of 17450 mm Hg; how many grams of N2 do you have in the vessel?
  88. chemistry

    Equilibrium is established between Br2(l) and Br2(g) at 25.0 (degrees)C. A 250.0 ml sample of the vapor weighs 0.486g. What is the vapor pressure of bromine at 25.0 (degrees)C, in millimeters of mercury.
  89. chemistry

    a gas occupies a volume of 50.0mL at degrees Celsius and 630mmHg.at what temperature in degrees Celsius would the pressure be 101.3kPa if the volume remains constant?
  90. chemistry

    A sample of gas occupies 17mL at -112 degrees Celsius. Assuming the pressure is held constant, what volume does the sample occupy at 70 degrees Celsius?
  91. chemistry

    A high-altitude balloon contains 97.5 L of helium gas at 95.8 kPa. What is the volume when the balloon rises to an altitude where the pressure is only 21.5 kPa? (Assume that the temperature remains constant.)
  92. Chemistry

    An experiment shows a 144mL sample of gas has a mass of 0.173g at a pressure of 720mmHg at a temperature of 31 degrees celsius. what is the molar mass of the sample of gas?
  93. Chemistry

    The gaseous product of a reaction is collected in a 25 L container at 27 degrees Celsius. The pressure in a container is 300 kPa and the gas has a mass of 96 g. What is the formula mass of the gas?
  94. Chemistry

    A sample gas has a volume of 200 cm^3 at 25 degrees celsius and 700 mmHg. If the pressure is reduced to 280 mmHg, what volume would the gas occupy at the same temperature?
  95. CHEMISTRY

    At 285mmHg +25 degrees celsius,a gas sample has a volume of 2270ml. what is the final pressure in mmHg at a volume of 1250ml and a temperature od 175 degrees celsius?
  96. Chemistry

    The volume of 02 collected over water at 25 degree C and 740 torr, was 250 mL. What volume will the dry 02 occupy at STP? (Vapor pressure of water at 25 degre C is 23.8 torr).
  97. chemistry

    a gas occupies a volume of 5.00L at 27 degreesC and 742 mmHg. if the volume is held constant and the temperature is increased by 2 degreesC, what is the final pressure of the gas?
  98. Chemistry

    Octane has a vapor pressure of 40 torr at 45.1 degrees Celsius and 400 torr at 104 degrees Celsius. What is its heat of vaporization? (Given R=8.314J/mol*K) Please explain.
  99. chemistry

    2. Zinc metal reacts with HCL similarly to magnesium: Zn(s) + 2HCL(aq) = ZnCl2(aq) + H2(g). the H2 gas produced was collected over water at 25 degrees Celsius and had a volume of 7.80L at 0.980 atm. How many grams of Zn were consumed in the reaction?
  100. chemistry

    Benzene has a heat of vaporization of 30.72kj/mol and a normal boiling point of 80.1 C . At what temperature does benzene boil when the external pressure is 410 ? This is how I am solving this problem, ln(415/760)= (30720/8.314)*(1/80.1 - 1/T2) It is