Jumpin’ Jack Flash It’s a gas gas gas! Solids, Liquids and Gases and Gas Laws Chapter 7

Solids, liquids and Gases At the end of this section you should be able to: use the kinetic theory of matter to explain properties of gases, liquids and solids describe the qualitative effect on gases of changes in pressure, volume and temperature describe the changes in temperature, potential energy and kinetic energy when a substance undergoes phase changes explain the factors that affect the vapour pressure of a liquid explain the relationship between vapour pressure and boiling temperature use the Kinetic Theory of Matter to explain relationship between heat and temperature change of phase vapour pressure and factors that affect vapour pressure effect on gases of changes in pressure, temperature and volume the characteristics of gases predict the effect on gases of changes in pressure, temperature and volume (qualitative only) explain the boiling point of a liquid. From the 2AB Chemistry Course Outline Gases, liquids and solids Behaviour of gases − kinetic theory Gas pressure, volume and temperature Volume and amount of gas Liquids and solids Changes in state Evaporation, vapour pressure and boiling Pure substances and mixtures

Characteristics of Gases Try thinking of a gas Air is a good one Can you list some of the gases that make up air? N 2 O 2 CO 2 H 2 Ne He Ar From which kind of element are these all made up? Think about the particles of a gas What do they look like? Are they big? Small?

Characteristics of Gases How would you describe a gas  what it does?  what it looks like?  shape?  behaviour?  how did it get to be a gas? What would be the best description you could give a gas? What are some ideas we use to describe what gases do? Pressure Volume Temperature How much (number of moles) Any more?

Kinetic Theory of Gases What do each of these words mean? KINETIC THEORY of GASES Ideal gas - what is this? All gases behave in generally the same manner*, so we can generalise their behaviour and devise a set of rules to predict and describe this behaviour THE GAS LAWS

Kinetic Theory of Gases So which gas is an ideal gas? Well… none of them are Why? Recall “All gases behave in generally the same manner*...” this is generally true for a limited set of circumstances - for a limited set of values for… PRESSURE VOLUME TEMPERATURE NUMBER OF MOLES

Kinetic Theory of Gases Model of Gas motion

What causes the pressure of a gas in a closed container? Impacts of gas molecules with the walls of the container. Anything that increases the number of impacts per second or the force of each impact increases the pressure. Impacts of gas molecules with the walls of the container. Anything that increases the number of impacts per second or the force of each impact increases the pressure. Microscopic View

Light molecules move faster and hit the walls more often. Heavy molecules hit the walls with lower velocity and less frequency, but the same force. These 2 effects exactly balance out. **Gas pressure doesn’t depend on the identity of the gas.**

1. Gases consist of tiny particles called molecules, except for the noble gases which consist of atoms Kinetic Theory of Gases The kinetic theory of gases is the best approximation of the way gases behave. Its description of gases is based on the following assumptions 2. The average distance between the molecules of a gas is large compared with the size of each gas molecule 3. The molecules of a gas move in rapid, random, straight line motion. These movements result in collisions with each other and with the sides of the container 4. The molecules of a gas exert negligible attractive or repulsive forces on one another 5. All collisions of gas molecules are perfectly elastic. This means there is no net energy loss during these collisions 6. The kinetic energy of the molecules increases with temperature 1. GASES R TINY 2. Little gas, lotsa space 3. Random, rapid, straight  collisions 4. No attraction / repulsion 5. Collisions elastic 6. T  KE 

Pressure Depends on 1) the concentration or # of gas molecules per unit volume and 2) the temperature.

How fast do the molecules in the air move? Depends on the mass. Depends on the mass. Light molecules are faster than heavy molecules at the same temperature. Light molecules are faster than heavy molecules at the same temperature. Temperature = measure of the ave. translational K.E. of the particles of a system. Temperature = measure of the ave. translational K.E. of the particles of a system.

Molecular Speeds at 298 K H X 10 5 cm/sec H X 10 5 cm/sec He1.36 X 10 5 cm/sec He1.36 X 10 5 cm/sec O X 10 4 cm/sec O X 10 4 cm/sec Ar4.31 X 10 4 cm/sec Ar4.31 X 10 4 cm/sec Xe2.38 X 10 4 cm/sec Xe2.38 X 10 4 cm/sec

HOW IS KINETIC ENERGY DISTRIBUTED IN A LIQUID?

LOW kinetic energy HIGH kinetic energy

LOW kinetic energy HIGH kinetic energy

LOW kinetic energy HIGH kinetic energy

LOW kinetic energy HIGH kinetic energy

LOW kinetic energy HIGH kinetic energy

LOW kinetic energy HIGH kinetic energy

LOW kinetic energy HIGH kinetic energy

LOW kinetic energy HIGH kinetic energy HOT COLD

LOW INTERMEDIATE HIGH kinetic kinetic kinetic energy energy energy COLDHOT

How many water molecules have intermediate K.E.? LOW INTERMEDIATE HIGH kinetic kinetic kinetic energy energy energy COLDHOT How many water molecules have HIGH K.E.? How many water molecules have LOW K.E.?

LOW kinetic energy HIGH kinetic energy INTERMEDIATE kinetic energy

Number of particles

kinetic energy lowhigh

low K.E. high K.E. average K.E. = temperature of liquid Number of particles

WHAT HAPPENS TO A LIQUID’S TEMPERATURE DURING EVAPORATION?

temperature of liquid low temperature high temperature

lowhigh temperature 1

lowhigh temperature 2

lowhigh temperature 2

Molecular Speed vs. Temperature

Pressure – Microscopic View Gas molecules hit the walls of their container. Gas molecules hit the walls of their container. Pressure depends on Pressure depends on  Number of impacts per unit time  Force of each impact

Pressure – Macroscopic View Pressure depends on how many gas molecules per unit volume and on the temperature. Pressure depends on how many gas molecules per unit volume and on the temperature. The same amount of gas exerts different pressure at different temperatures (tires). The same amount of gas exerts different pressure at different temperatures (tires).

Avogadro’s Law Equal volumes of gases at the same pressure and temperature contain the same number of “particles.” V = an where V = volume of the gas, n= # of moles of gas, & a is a constant.

3 containers – same size, same temperature, same pressure. Box A He Box B N 2 Box C CH 4 What can you say about the number of molecules in each box? It’s the same. B = 2 X A C = 5 X A B = 2 X A C = 5 X A What can you say about the number of atoms in each box?

Boyle’s Law

Boyle’s Law - words The volume of a sample of gas is inversely proportional to its pressure, at constant temperature. The volume of a sample of gas is inversely proportional to its pressure, at constant temperature.

Scientists plot data because a picture shows relationships better than lists of numbers. There are lots of “pictures” that scientists & mathematicians recognize.

Boyle’s Law - mathematically P X V = K, a constant V = K/P or P = K/V P 1 V 1 = P 2 V 2 For every point on the hyperbola, P X V = the same constant, K

PV vs. P Pressure (atm) PV CO 2 Ne O2O2 Ideal

Boyle’s Law Problems The plunger of a bicycle pump is pushed in so that the pressure of the trapped air changes from 1.65 atm to 2.50 atm. No air can escape. Temperature is constant. The initial volume of air is L. Calculate the final volume. Graph the following data set and comment on whether it follows Boyle’s Law behaviour

Charles’ Law The volume of a gas at constant pressure varies directly with its absolute temperature.

Linear Relationship Plot Volume vs.  C and you get a straight line. The relationship between Volume and  C is linear. The equation of a line is: Y = mX + b.

Charles extrapolated the graph to 0 volume. At 0 mL, the X-intercept is  C.

Hints of Kelvin scale Charles extrapolated his data to see the temperature at which the volume was 0. 1st indication that the temperature -273  C might have a fundamental meaning. Why did Charles have to extrapolate his lines in this temperature range instead of taking data?

Charles’ Law: Graphically Plot Volume vs. Kelvin Temperature Straight line that passes through the origin. V = kT or V = k or V 1 /T 1 = V 2 /T 2 T

Volume Temperature He CH 4 H2OH2O H2H2 N2ON2O  C

Charles’ Law A sample of a gas at 125  C and 1 atm pressure occupies a volume of 55.8 liters. What volume will the it occupy at -45  C?

Gas laws summary

Behaviour of Real Gases

Under pressure Double click on on the spreadsheet and play around with the numbers to investigate the effect of changing different gas law parameters