Question

1.Answer the following with an explanation using both words and a picture.

a. If a fixed amount of gas at a constant temperature has its pressure increased, what happens to the volume of the gas? Why? Explain what’s happening using both words and a picture.

b. If a fixed amount of gas at a constant pressure has its volume decreased, what happens to the Kelvin temperature of the gas? Why? Explain what’s happening using both words and a picture.

c. If a fixed amount of gas at a constantvolumehas its Kelvin temperatureincreased, what happens to the pressureof the gas? Why? Explain what’s happening using both words and a picture.

d. If a gas at a constant temperature and pressure has the number of moles of gas decreased, what happens to the volume of the gas? Why? Explain what’s happening using both words and a picture.

Answer 1

a) Scenario 1- temperature constant.

According to Boyle's law, at constant temperature, the volume of a given amount of gas is inversely proportional to the pressure of it. So a fixed amount of gas at a constant temperature increased it's pressure means the volume of the gas decreased. If the volume of the gas decreases but the amount remains fixed that means now the same mole of gas is occupying less space, as a result Brownian motion and collision of the gas molecules with the surrounding walls of the container increases which causes an increase of pressure.

b) Scenario 2- pressure constant.

According to Charles' law, volume of a given amount of gas at constant pressure is directly proportional to the Kelvin temperature. So if we decrease the volume then the Kelvin temperature also decreases as the gas is maintaining constant pressure so now the gas molecules have to maintain the same pressure even being within a shorter space so they have to decrease their motion and kinetic energy which is only possible if the temperature also decreases and the system becomes cooler.

c) Scenario 3- constant volume

According to the Gay-Lussac law, the pressure of a given amount of gas held at constant volume is directly proportional to the Kelvin temperature. So if we increase the Kelvin temperature of a fixed volume of gas then pressure of the gas will increase. Increasing the Kelvin temperature i.e. heating the gas gives the molecules more and more kinetic energy and they move faster. Which means more and more impact on the walls of the container as a result increase of pressure.

d) Scenario 4- Constant temperature and pressure.

According to Avogadro's law, at constant temperature and pressure, if the amount of gas (number of moles) in a container is increased then the volume will increase. If the amount of gas in a container is decreased then the volume decreases. If the number of moles decreases then to maintain the constant pressure and temperature the volume has to decrease otherwise both pressure and temperature will decrease.