Pressure is defined as the force exerted on a surface divided by the area of that surface.
Correct Answer
True
True. Pressure is force per unit area, so the same force spread over a larger area gives a lower pressure. The SI unit, the pascal, equals one newton per square meter.
Category: Gas Pressure
Question 2
Atmospheric pressure increases as altitude increases.
Correct Answer
False
False. Atmospheric pressure decreases as altitude increases, because there is less air above pressing down. This is why air pressure on a mountaintop is well below 1 atm.
Category: Gas Pressure
Question 3
A pressure of 1 atm is about 14.7 pounds per square inch.
Correct Answer
True
True. Standard atmospheric pressure at sea level is about 14.7 psi, the same pressure as 760 torr or 101.325 kPa. Tire gauges in the United States read in psi above atmospheric pressure.
Category: Gas Pressure
Question 4
Boyle's law states that at constant temperature and amount, the volume of a gas is directly proportional to its pressure.
Correct Answer
False
False. Boyle's law states that volume is inversely proportional to pressure at constant temperature and amount, so PV stays constant. Doubling the pressure halves the volume.
Category: Simple Gas Laws
Question 5
When a gas law calculation uses temperature, the temperature must be expressed in kelvins.
Correct Answer
True
True. The gas laws treat volume and pressure as proportional to absolute temperature, which only works on a scale that starts at absolute zero. Celsius values must be converted by adding 273.15.
Category: Simple Gas Laws
Question 6
Absolute zero, the temperature at which an ideal gas would have zero volume, is 0 degrees Celsius.
Correct Answer
False
False. Absolute zero is 0 K, which is -273.15 degrees Celsius. Extending a plot of gas volume against Celsius temperature to zero volume crosses the axis at this value.
Category: Simple Gas Laws
Question 7
In the equation PV = nRT, the symbol n stands for the mass of the gas in grams.
Correct Answer
False
False. In the ideal gas law, n is the amount of gas in moles. To use a mass in grams, first divide it by the molar mass to get moles.
Category: Ideal Gas Law
Question 8
At constant pressure, the density of a gas increases as its temperature increases.
Correct Answer
False
False. Gas density equals PM/RT, so at constant pressure density decreases as temperature rises. Heating a gas spreads the same mass over a larger volume, which is why hot air rises.
Category: Ideal Gas Law
Question 9
A sample of an ideal gas at fixed temperature and pressure has a volume that depends only on its number of moles, not on which gas it is.
Correct Answer
True
True. Rearranging PV = nRT gives V = nRT/P, which contains no term for the identity of the gas. One mole of hydrogen and one mole of carbon dioxide occupy the same volume under the same conditions if both behave ideally.
Category: Ideal Gas Law
Question 10
In a gas mixture, the component with the largest mole fraction has the largest partial pressure.
Correct Answer
True
True. Each partial pressure equals the component's mole fraction times the total pressure, so partial pressures rank in the same order as mole fractions. The gas with the most moles exerts the largest share of the pressure.
Category: Mixtures and Stoichiometry
Question 11
The mole fractions of all the components in a gas mixture add up to 1.
Correct Answer
True
True. Each mole fraction is the moles of one component divided by the total moles, so together they account for the whole mixture and sum to 1. This is why the partial pressures add up to the total pressure.
Category: Mixtures and Stoichiometry
Question 12
Adding helium to a rigid container of oxygen at constant temperature changes the partial pressure of the oxygen.
Correct Answer
False
False. In a rigid container at constant temperature, the oxygen's partial pressure depends only on its own moles, the volume and the temperature, none of which change. The added helium raises the total pressure, not the oxygen's partial pressure.
Category: Mixtures and Stoichiometry
Question 13
Diffusion is the gradual mixing of one gas through another as a result of the random motion of their molecules.
Correct Answer
True
True. Diffusion is the spreading of gas molecules through a space or another gas, such as a perfume scent moving across a room. It is slower than molecular speeds suggest because molecules constantly collide and change direction.
Category: Effusion and Diffusion
Question 14
Graham's law states that the rate of effusion of a gas is inversely proportional to its molar mass.
Correct Answer
False
False. Graham's law states that the rate of effusion is inversely proportional to the square root of the molar mass. A gas with one fourth the molar mass effuses twice as fast, not four times as fast.
Category: Effusion and Diffusion
Question 15
At the same temperature, NH3 diffuses faster than HCl.
Correct Answer
True
True. NH3 has a molar mass of about 17 g/mol and HCl about 36.5 g/mol, so NH3 molecules move faster on average. When the two gases diffuse toward each other in a tube, the white NH4Cl ring forms closer to the HCl end.
Category: Effusion and Diffusion
Question 16
Kinetic-molecular theory assumes that gas molecules take up most of the volume of their container.
Correct Answer
False
False. Kinetic-molecular theory assumes the molecules themselves occupy a negligible fraction of the container volume, which is mostly empty space. This is why gases are so easily compressed.
Category: Kinetic-Molecular Theory
Question 17
At the same temperature, O2 molecules have a greater average kinetic energy than H2 molecules.
Correct Answer
False
False. At the same temperature, all gases have the same average kinetic energy. The heavier O2 molecules move more slowly than H2 molecules, which balances their larger mass.
Category: Kinetic-Molecular Theory
Question 18
Adding more gas to a rigid container at constant temperature raises the pressure because molecules strike the walls more often.
Correct Answer
True
True. With more molecules in the same volume, more collisions with the walls occur each second, and pressure is the result of those collisions. The average force of each collision stays the same because the temperature has not changed.
Category: Kinetic-Molecular Theory
Question 19
For an ideal gas, the compressibility factor PV/nRT equals 1 at all pressures.
Correct Answer
True
True. An ideal gas obeys PV = nRT exactly, so the ratio PV/nRT is always 1. Real gases show values above or below 1, and the size of the departure measures how far they are from ideal behavior.
Category: Real Gases
Question 20
Attractions between molecules make the pressure of a real gas higher than the pressure predicted for an ideal gas.
Correct Answer
False
False. Intermolecular attractions pull molecules back slightly as they approach the walls, so they hit with less force and the real pressure is lower than the ideal prediction. The van der Waals a term corrects for this effect.
Category: Real Gases