Chapter 14 “The Behavior of Gases” Chemistry Level 2

Variables That Describe a Gas The four variables and their common units: 1.pressure (P) Kilopascals, mm Hg, atmospheres, Torr 2. volume (V) Liters, mL, or cubic units 3. temperature (T) in Kelvin 4. amount (n) in moles The amount of gas, volume, and temperature are factors that affect gas pressure.

1. Amount of Gas When we inflate a balloon, we are adding gas molecules. Increasing the number of gas particles increases the number of collisions – thus, the pressure increases If temperature is constant- doubling the number of particles doubles the pressure

2. Volume of Gas In a smaller container, the molecules have less room to move. The particles hit the sides of the container more often. As volume decreases, pressure increases. (think of a syringe)

3. Temperature of Gas Raising the temperature of a gas increases the pressure, if the volume is held constant. – The molecules hit the walls harder, and more frequently! Fig. 14.7, page 417 Should you throw an aerosol can into a fire? What could happen? When should your automobile tire pressure be checked?

#1. Boyle’s Law Pressure x Volume = a constant Equation: P 1 V 1 = P 2 V 2 (T = constant) Gas pressure is inversely proportional to the volume, when temperature is held constant.

Graph of Boyle’s Law – page 418

#2. Charles’s Law The volume of a fixed mass of gas is directly proportional to the Kelvin temperature, when pressure is held constant. This extrapolates to zero volume at a temperature of zero Kelvin. V 1 = V 2 P = (constant) T 1 T 2

Converting Celsius to Kelvin Gas law problems involving temperature will always require that the temperature be in Kelvin. (Remember that no degree sign is shown with the kelvin scale.) Reason? There will never be a zero volume, since we have never reached absolute zero. Kelvin =  C °C = Kelvin and