Changes in Gas pressure Chapter 8.4 con’t

Variables Pressure Volume Temperature

Pressure and Volume What happens when you squeeze a balloon? How does the volume change? How does the pressure change?

Boyle’s Law When the volume of a gas decreases, the pressure of the gas increases. When the volume of a gas increases, the pressure of the gas decreases Only works for a fixed amount of gas with a constant TEMPERATURE

What do you think is going to happen to the volume of the air bubbles as they rise to the surface?

Boyle’s Law Equation P 1 V 1 = P 2 V 2 Initial Pressure x Initial Volume = Final Pressure x Final Volume

P 1 V 1 = P 2 V 2 What happens to the pressure when the volume of a container is cut in half? What happens to the pressure then the volume of a container is doubled?

Boyle’s Law

Pressure and Temperature

Kelvin Temperature Scale Naturally, gases don’t really reach a 0 volume, but the spaces between molecules approach 0. At this point all molecular movement stops. –273C is known as “absolute zero” (no E K ) Lord Kelvin suggested that a reasonable temperature scale should start at a true zero value. He kept the convenient units of °C, but started at absolute zero. Thus, K = °C °C = ? K: K=°C+273 = = 335 K Notice that kelvin is represented as K not °K.

Practice Kelvin Conversion O°C = _____ K 100°C = ______K 100 K = _____ °C -30 °C = ______ K 300 K = _____ °C 403 K = _______°C 25 °C = ______ K O K = _______°C

Charles’ Law When the temperature of a gas increases, the volume of the gas increases. When the temperature of a gas decreases, the volume of the gas decreases. This works if the PRESSURE and the number of particles remain the same.

This should sound familiar to you.....KMT As a gas is heated, its particles move faster and its temperature increases Because the gas particles move faster and faster, they begin to strike the walls of their container more often and with more force. If the walls are free to move, the gas pushes the walls out and expands.

Charles’s Law

Charles’s Law Equation The temperature must be expressed in kelvins! V 1 = V 2 T 1 T 2

What happens to the volume when the temperature decreases?