Starter S-146 List five properties of gases.

The Behavior of Gases Chapter 14

14.1 Properties of Gases Chapter 14

Gases are easily squeezed into a smaller volume Compressibility – how much the volume decreases under pressure Air bags can absorb energy by compressing a gas 14.1 Properties of Gases

Gases can be compressed because the actual particles take up very little of the volume 14.1 Properties of Gases

Four variables are used to describe gases 1.Pressure (P) – force per unit area on the container 2.Volume (V) – in liters, how much space the gas take up 3.Temperature (T) – average kinetic energy 4.Number of Moles (n) – how much of the gas is present 14.1 Properties of Gases

14.2 The Gas Laws Chapter 14

Robert Boyle Boyle’s Law – If temperature is kept constant, as pressure increases the volume decreases So if T is constant or 14.2 The Gas Laws

Since the equation is equal to a constant This is used to compare values as long as the temperature and the number of moles remain constant 14.2 The Gas Laws

Jacques Charles Charles’s Law – If pressure is kept constant, as temperature increases, volume also increases That is or 14.2 The Gas Laws

Since the equation is equal to a constant This is used to compare values as long as the pressure and the number of moles remain constant Temperature must always be calculated in Kelvin in all gas calculations 14.2 The Gas Laws

Joseph Gay-Lussac Gay-Lussac’s Law – If volume is constant, when the temperature increases, pressure increases That is or 14.2 The Gas Laws Simulation

Since the equation is equal to a constant This is used to compare values as long as the volume and the number of moles remain constant Temperature is in Kelvin 14.2 The Gas Laws

Combined Gas Law – all three relationships are combined into This equation can be used to solve relationships that involve any combination of these three variables Just remove any variable that does not change 14.2 The Gas Laws

Example – a sample of oxygen gas at STP is heated to 50.0 o C at a constant volume, what is the new pressure? What stays constant? 14.2 The Gas Laws

Example – If 40.0 mL of nitrogen gas at 812mmHg and 75.0 o C is cooled to o C and has the pressure reduced to 125mmHg, what is the new volume? 14.2 The Gas Laws

14.3 Ideal Gas Chapter 14

Avogadro’s Law – if the temperature and pressure are held constant, an increase in gas particles (moles) will cause an increase in the volume This can be written as 14.3 Ideal Gas Simulation

The ideal gas law combines all the laws into one equation R is a constant Usually written as 14.3 Ideal Gas

A container has 2,240,000 L of methane gas (CH4) at a pressure of 1500 kPa and a temperature of 42 o C. A.How many moles of gas are in the container? B.How many grams of gas are in the container? 14.3 Ideal Gas

An ideal gas – is an imaginary gas that always follows the ideal gas law In a real gas 1.Particles take up volume 2.Force exist between particles So real gases deviate from the an ideal gas especially at 1.Low temperature 2.High pressure 14.3 Ideal Gas

14.4 Gases: Mixtures and Movements Chapter 14

Dalton’s Law of Partial Pressure – in a mixture of gases, the total pressure is the sum of the partial pressures of the gases Since the temperatures and volumes must be the same for each gas All that matters is the number of moles of gas present 14.4 Gases: Mixtures and Movements

Dalton’s Law of Partial Pressure – in a mixture of gases, the total pressure is the sum of the partial pressures of the gases Since the temperatures and volumes must be the same for each gas All that matters is the number of moles of gas present 14.4 Gases: Mixtures and Movements

The total air pressure is the sum of the partial pressures of the different gases 14.4 Gases: Mixtures and Movements Composition of Dry Air ComponentVolume (%)Partial Pressure (kPa) Nitrogen Oxygen Carbon Dioxide0.04 Other Gases Total

The minimum partial pressure of oxygen needed for a human is about 16kPa Partial pressures are written with a subscript This can be calculated using the ideal gas law 14.4 Gases: Mixtures and Movements

Thomas Graham Diffusion – tendency of particles to move toward areas of lower concentration Effusion - is the process in which individual molecules flow through a hole without collisions between molecules 14.4 Gases: Mixtures and Movements Simulation

Graham’s Law of Effusion – the rate of effusion of a gas is inversely proportional to the square root of the gas’s molar mass Can be written If two objects are at the same temperature they must have the same kinetic energy 14.4 Gases: Mixtures and Movements

So a larger molecule must be moving slower 14.4 Gases: Mixtures and Movements