Boyle’s Law Charles’ Law Gay-Lussac’s Law The Gas Laws Boyle’s Law Charles’ Law Gay-Lussac’s Law

Behavior of Gases 16.3 Pressure Pressure is the amount of force exerted per unit of area, or P = F/A. A balloon and a bicycle tire are considered to be containers. They remain inflated because of collisions the air particles have with the walls of their container.

Behavior of Gases 16.3 Pressure This collection of forces, caused by the collisions of the particles, pushes the walls of the container outward. If more air is pumped into the balloon, the number of air particles is increased. This causes more collisions with the walls of the container, which causes it to expand.

Behavior of Gases 16.3 Pressure Pressure is measured in a unit called Pascal (Pa), the SI unit of pressure, but we’ll use kPa, or kiloPascals. At sea level, atmospheric pressure is 101.3 kPa. Unit for pressure = kPa

Behavior of Gases 16.3 Boyle’s Law What happens to the gas pressure if you decrease the size (volume) of the container? If you squeeze gas into a smaller space, its particles will strike the walls more often giving an increased pressure. The opposite is true, too. Lower volume = higher pressure Higher volume = lower pressure

Behavior of Gases 16.3 Boyle’s Law Robert Boyle (1627-1691), a British scientist, described this property of gases. According to Boyle’s law, if you decrease the volume of a container of gas and hold the temperature constant, the pressure of the gas will increase. An increase in the volume of the container causes the pressure to drop, if the temperature remains constant.

Behavior of Gases 16.3 Boyle’s Law Boyle’s law states that as pressure is decreased the volume increases. The opposite also is true, as shown by the graph. As the pressure is increased, the volume will decrease.

Behavior of Gases 16.3 Boyle’s Law in Action When Boyle’s law is applied to a real life situation, we can predict the new volume or new pressure of a gas mathematically.

Behavior of Gases 16.3 Boyle’s Law in Action You can use the equation P1V1 = P2V2 to express this mathematically. P1 = initial pressure (in kPa) V1 = initial volume (in L) P2 = new pressure (in kPa) V2 = new volume (in L)

Example 15 L of gas has a pressure of 3 kPa. The pressure is increased to 5 kPa. What is the new volume of the gas?

Behavior of Gases 16.3 Charles’s Law Jacques Charles (1746-1823) was a French scientist who studied gases. According to Charles’s law, the volume of a gas increases with increasing temperature, as long as pressure does not change.

Charles’s Law 16.3 As with Boyle’s law, the reverse is true, also. Behavior of Gases 16.3 Charles’s Law As with Boyle’s law, the reverse is true, also.

Behavior of Gases 16.3 Charles’s Law Charles’s law can be explained using the kinetic theory of matter. As a gas is heated, its particles move faster and faster and its temperature increases. Because the gas particles move faster, they begin to strike the walls of their container more often and with more force.

Behavior of Gases 16.3 Using Charles’s Law The formula that relates the variables of temperature to volume shows a direct relationship, V1/T1 = V2/T2, when temperature is given in Kelvin (pressure remains constant). To convert from Celsius to Kelvin, simply add 273 to the Celsius temperature. Example: 10̊C + 273 = 283 K

Behavior of Gases 16.3 Using Charles’s Law What would be the resulting volume of a 2.0-L balloon at 25.0C that was placed in a container of ice water at 3.0C?

Behavior of Gases 16.3 Using Charles’s Law As Charles’s law predicts, the volume decreased as the temperature of the trapped gas decreased.

The Pressure-Temperature Relationship Behavior of Gases 16.3 The Pressure-Temperature Relationship What happens if you heat an enclosed gas? The particles of gas will strike the walls of the canister more often. Why? If the pressure becomes greater than the canister can hold, it will explode. At a constant volume, an increase in temperature results in an increase in pressure.

Pressure and Temperature Joseph Louis Gay-Lussac was a French professor who studied the behavior of gases with many scientists. In the early 1800s, he observed a relationship between the pressure and temperature of gases.

Gay-Lussac’s Law Just like Charles’ law, Gay-Lussac’s law describes a direct relationship between two variables (as one increases, so does the other). According to the law, as the temperature of a gas increases, so does the pressure (as long as the volume remains constant). As the temperature decreases, so does the pressure (as long as the volume remains constant).

Mathematically speaking… We can look at this law mathematically. P1/T1 = P2/T2 P1 = initial pressure (in kPa) T1 = initial temperature (in K) P2 = new pressure (in kPa) T2 = new temperature (in K)

Example A gas in an aerosol can has a temperature of 30̊C and a pressure of 3 kPa. If the temperature is increased to 45̊C, what will the new pressure of the gas be? Don’t forget to convert ̊C to K first. 

Section Check 16.3 Question 1 What would be the resulting volume of a 3.0-L balloon at 25.0º C that was placed in a container of ice water at 4.0º C, if pressure is constant? A. 2.8 L B. 3.0 L C. 4.8 L D. 5.0 L

Section Check 16.3 Answer The answer is A. Use the formula that relates volume to temperature given in Kelvin, V1/T1 = V2/T2. In this case, V1 = 3.0 L, T1 = 25.0º C + 273 = 298º K, T2 = 4.0º C + 273 = 277º K. Solving for V2 gives 2.8 L.

Section Check 16.3 Question 2 The SI unit of pressure is the pascal, but we use the _________. A. coulomb B. tesla C. Watt D. kiloPascal

Section Check 16.3 Answer The answer is D. The SI unit of pressure is the Pascal; we measure pressures in kiloPascals.