10.4 Buoyancy, volume, temperature, and pressure of

gases A hot-air balloon floats because the air inside is less dense than the air outside.

The balloon example illustrates an important relationship, known as Charles’s law, discovered by Jacques Charles in 1787.

10.4 Charles’ Law According to Charles’ law, the volume of a

gas increases with increasing temperature. Volume decreases with decreasing

temperature.

10.4 Pressure-Temperature Relationship

The pressure of a gas is also affected by temperature changes.

If the mass and volume are kept constant, the pressure goes up when the temperature goes up, and the pressure goes down when the temperature goes down.

10.4 Pressure-Temperature Relationship

The mathematical relationship between the temperature and pressure of a gas at constant volume and mass was discovered by Joseph Gay-Lussac in 1802.

10.4 Converting to KelvinAny time you see a temperature in a formula in this section about gases, the temperature must be in Kelvins.

Solving Problems

A can of hair spray has a pressure of 300 psi at room temperature 21°C.

The can is accidentally moved too close to a fire and its temperature increases to 295°C.

What is the final pressure in the can? (Round answer to nearest whole number.)

1. Looking for: …final pressure in psi(P2)

2. Given …P1= 300 psi, T1 = 21 C , T2 = 295 C

3. Relationships: Convert temps using K = C + 273 Charles’ Law: P1/T1 = P2/T2

4. Solution Rearrange equation so P2 = P1xT2 / T1

P2 = 300 psi. x 568K / 294K = 580 psi.

Solving Problems