Aim: How do gas molecules react to pressure, volume and temperature? Warm Up: What are characteristics of gas molecules?

Let’s Go Scuba Diving

Properties of Gases (Review) No definite shape No definite volume compressible

Kinetic Molecular Theory moving molecules well supported ideas

Basic Kinetic Theory of Gases Composed of particles like atoms (ex: He) or molecules like (O2 and CO2) There are no attractive/repulsive forces. Lots of empty space!!

Basic Kinetic Theory of Gases 2. Particles move in random, constant, straight-line motion. Move independently of each other.

Basic Kinetic Theory of Gases 3. All collisions are elastic meaning that KE is transferred without loss of energy. No change in kinetic energy. Gases tend to diffuse towards areas of lower concentration.

Gas Pressure Pressure- force exerted on container walls by particles in a gas Units used- kPa, atm, Torr, mmHg STP (Standard Temperature and Pressure) Table A 273 K or 0°C and 101.3 kPa = 1 atm = 760 Torr (mmHg)

Factors Affecting Pressure Amount of Gas (number of moles) Increasing amount will increase P (and vice versa) Ex: bicycle tires, car tires Temperature Increasing temp. will increase P (and vice versa) Ex: Tires deflate in winter Volume Decreasing volume will increase P, increasing volume decreases P Ex: press down on a balloon and it pops

Boyle’s Law Pressure and volume have an inverse relationship, if temperature remains constant. If volume is increased, pressure is decreased by the same factor.

Mathematically, the product of PV is constant or PV = k (where k is some constant). Boyle’ Law P1 V1 = P2 V2 = P3 V3…

Summary

Charles’ Law Volume and temperature have a direct relationship, if pressure is held constant. If temperature (K) is increased, volume is increased by the same factor.

Mathematically, the relationship of volume divided by Kelvin temperature is constant or V/T = k. Charles’ Law V1 /T1 = V2 /T2 = V3 /T3 …

Summary

Gay – Lussaic’s Law Pressure and temperature have a direct relationship, if volume remains constant. If temperature (K) is increased, pressure will be increased by the same factor.

Mathematically, the relationship of volume divided by Kelvin temperature is constant or P/T = k. Gay-Lussac’s Law P1 /T1 = P2 /T2 = P3 /T3 … Pressure

Avogadro’s Law Avogadro’s number: 6.02 x 1023 Simply refers to the quantity of particles found in a mole. At STP, 6.02 x 1023 particles of a gas occupies 22.4 L. At STP, 3.01 x 1023 particles of a gas occupies 11.2 L.

Avogadro also hypothesized that equal volumes of different gases at the same temperature and pressure contain equal number of particles (or equal moles).

AIM: How do we use the combined gas law?

Ideal Gases vs. Real Gases “Ideal gases” behave as predicted by Kinetic Molecular Theory. Examples: H2 and He Gases are most ideal at high temperature and low pressure (also have low mass and low polarity).

“Real gases” deviate from ideal behavior. Why? At low temps, gas particles become attracted to each other (KMT says they are not). Under high pressure, gases occupy a specific volume, turn to a liquid (KMT says they don’t).

Lets try an example Under which conditions of temperature and pressure would helium behave most like an ideal gas? a. 50 K and 20 kPa b. 50 K and 600 kPa c. 750 K and 20 kPa d. 750 K and 600 kPa

Combined Gas Law Equation P1 V1 = P2 V2 T1 T2

Combined Gas Law Equation Steps: Determine which variable (if any) is kept constant. Cancel those terms and remove them from the equation (Ex: If the question says that temperature remains constant the new equation becomes P1V1 = P2V2). Plug in values that are given. Solve for the unknown. Be sure to always use temperature in Kelvins.

Lets Practice If I initially have 4.0 L of a gas at a pressureof 1.1 atm, what will the volume be if I increase the pressure to 3.4 atm? What do we know? Who’s law is it?

A toy balloon has an internal pressure of 1. 05 atm and a volume of 5 A toy balloon has an internal pressure of 1.05 atm and a volume of 5.0 L. If the temperature where the balloon is released is 20°C, what will happen to the volume when the balloon rises to an altitude where the pressure is 0.65 atm and the temperature is –15°C? What do we know? Which gas law?

People who are angry sometimes say that they feel as if they’ll explode. If a calm person with a lung capacity of 3.5 liters and a body temperature of 36°C gets angry, what will the volume of the person’s lungs be if their temperature rises to 39°C. Based on this, do you think it’s likely they will explode? What do we know and whos law is it?

Vapor Pressure In a sealed container, vapor pressure can be measured above a liquid. Evaporation occurs when some particles from the surface of a liquid escape causing pressure to build up above the liquid (not to be confused with boiling).

Factors that Increase the Rate of Evaporation Heating a liquid (not to boiling point) Increasing surface area Create air currents (blow across the surface)

Liquid-Vapor Equilibrium Some of the gas particles condense and then we find both evaporating and condensing occurs at the same rate. Rate of Evaporation = Rate of Condensation

Related to Boiling Boiling occurs when the vapor pressure becomes equal to the external pressure. At normal atmospheric pressure, we call this normal boiling point.

Boiling and Attractive (Intermolecular Forces) Boiling occurs when heat energy overcomes attractive forces between molecules. The stronger the intermolecular forces, the higher the boiling point. The weaker the intermolecular forces, the lower the boiling point.

Table H Notice, increasing temperature increases vapor pressure. Line drawn at 101.3 kPa corresponds to normal boiling point.