Gas Laws

The Kinetic Molecular Theory Gas particles do not repel or attract each other. Gas particles are much smaller than the distances between them. Gas particles are in constant, random motion. No kinetic energy is lost when gas particles collide. All gases have the same kinetic energy at a given temperature.

Pressure Pressure is force applied over an area. For gases, the pressure is determined by the number of collisions with the walls of the container. Units: – atm: atmospheres – kPa: kiloPascal (= 1 N/m 2 ) – mmHg: millimeters of mercury – psi: pound force per square inch

The variables and their units VariableSymbolUnits PressurePatm VolumeVLiters Amount of gasnMoles TemperatureTKelvin

Conversion Factors Conversion for Pressure 1 Torr = 1 mm Hg

Conversion Factors Conversion for Temperature

STP

The Relationships Copy in color: 10 x 4 = 8 x ?? What is the missing number? From before to after: – How did the red number change? – How did the black number change? What is the math term for this relationship? Which two gas variables have this type of relationship? beforeafter

The Relationships Inversely proportional10 x 4 = 8 x ?? Pressure and volume P 1 V 1 = P 2 V 2

The Relationships Copy in color:? What is the missing number? From before to after: – How did the red number change? – How did the black number change? What is the math term for this relationship? Which two gas variables have this type of relationship? = beforeafter

The Relationships Directly proportional? Pressure and Temperature Volume and Temperature Volume and amount of gas =

The Combined Gas Law if every gas variable changed, this is the relationship Things that don’t change can cancel or drop out.

The Combined Gas Law if every gas variable changed, this is the relationship If amount of gas and volume stay the same, they cancel or drop out. Simplifies to

The Combined Gas Law if every gas variable changed, this is the relationship If amount of gas and temperature stay the same, they cancel or drop out. Simplifies to P 1 V 1 = P 2 V 2

Let’s Practice At 20°C, the volume of a gas is mL. The temperature is raised to 100°C. How do you expect the volume to change? It should increase Simplify the Combined Gas Law for this scenario. T1T1 V1V1 T2T2 Simplifies to

Let’s Practice At 20°C, the volume of a gas is mL. The temperature is raised to 100°C. T1T1 V1V1 T2T = 293K +273 = 373K V 2 = 127 mL Does this match your prediction? You said it would increase.

Let’s Practice 50.0 mL of a gas has a pressure of mmHg when it is in a container. The pressure changes to mmHg. How do you expect the volume to change? It should decrease Simplify the Combined Gas Law for this scenario. V1V1 P1P1 P2P2 Simplifies to P 1 V 1 = P 2 V 2

Let’s Practice 50.0 mL of a gas has a pressure of mmHg when it is in a container. The pressure changes to mmHg? V1V1 P1P1 P2P2 P 1 V 1 = P 2 V 2 (740.0mmHg)(50.0mL) = (760.0mmHg)V mL = V 2 Does this match your prediction? You said it would increase.