• Gas laws provide explanations for the relationships between:
  • Pressure and volume at a constant temperature
  • Pressure and (Kelvin) temperature at a constant volume

   

Pressure & Volume

• If the temperature of a gas remains?constant, the pressure of the gas changes when it is:
  • Compressed?– decreases the volume which?increases?the pressure
  • Expanded?– increases the volume which?decreases?the pressure

   

Pressure increases when a gas is compressed

• Similarly, a change in pressure can cause a change in volume
• A?vacuum pump?can be used to remove the air from a sealed container
• The diagram below shows the change in volume to a tied up balloon when the pressure of the air around it decreases:

• Therefore, if the gas is compressed, the molecules will hit the walls of the container?more frequently
  • This creates a larger overall?net force?on the walls which increases the?pressure

   

Pressure & Temperature

• The motion of molecules in a gas changes according to the?temperature
• As the temperature of a gas increases, the average?speed?of the molecules also?increases
• Since the average kinetic energy depends on their speed, the kinetic energy of the molecules also increases if its volume remains constant
  • The?hotter?the gas, the?higher?the average kinetic energy
  • The?cooler?the gas, the?lower?the average kinetic energy

   

• If the gas is heated up, the molecules will travel at a higher?speed
  • This means they will collide with the walls?more often
  • This creates an increase in?pressure

   

• Therefore, at a constant volume, an?increase?in temperature?increases?the pressure of a gas and vice versa
• Diagram A shows molecules in the same volume collide with the walls of the container more with an increase in temperature
• Diagram B shows that since the temperature is proportional to the pressure, the graph against each is a straight line

At constant volume, an increase in the temperature of the gas increases the pressure due to more collisions on the container walls