Unit 13 notes.notebook

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December 03, 2013

Nov 25­7:40 AM

Gas Laws NotesKinetic Molecular Theory: matter is made up of tiny particles that are always in motion; warm particles move faster than cold particles, so warm matter has more kinetic energy.

Kinetic Theory of gases is based on 5 assumptions:

1. Gases consist of large numbers of tiny particles that are far apart relative to their size.

2. Collisions between gas particles and between particles and container walls are elastic collisions.

3. Gas particles are in continuous, rapid, random motion.They therefore posses kinetic energy, which is energy of motion.

4. There are no forces of attraction or repulsion between gas particles.

5. The average kinetic energy of gas particles depends on the temperature of the gas.

Jan 8­6:47 AM

Properties of gases:

Expansion: No definite shape or volume. Expand to fill its container.

Compressibility: a measure of how much the volume of matter decreases under pressure. Gases are easily compressed because of the space between particles.

Low Density: particles are much farther apart in the gaseous state.

Fluidity: gas particles easily slide past one another, ability to flow.

Nov 25­7:52 AM

Pressure is the force exerted by a gas per unit surface area of an object.Standard Pressure is average normal air pressure at sea level.

As you go above sea level, air pressure is less.

Force is measured with a Newton.

Nov 25­8:03 AM

The SI unit of temperature is the Kelvin. A Kelvin is equal to the size of a Celsius

degree. However, Celsius is based on the freezing temperature of water and

Kelvin is based absolute zero. In both scales the freezing point and boiling point

of water are 100° apart.

The Fahrenheit scale is set up so that there are 180° between the boiling point and freezing point of water.

Conversions:°C = K ­ 273 K = °C + 273°F = (9/5)°C + 32 °C = 5/9(°F ­ 32)

Jan 8­6:48 AM

Standard Air Pressure: (all values equal to each other)

760 mmHg 760 torr 1.01325 x 105 Pa 101.325 kPa 1atm 1. Convert 421 torr to atm.

2. Convert 32.0 kPa to torr.

Jan 8­6:49 AM

Standard Temperature and Pressure (STP): 0°C 1 atm

The melting point and boiling point of substances can change when

the pressure changes. Pressure affects the ability of vapor particles

to escape. Phase diagrams show where the state changes occur at

different temperatures.

Unit 13 notes.notebook

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December 03, 2013

Jan 8­6:51 AM Jan 8­6:51 AM

Manometers and barometers are used to measure pressure. Open manometers compare gas pressure to air pressure.

Closed manometers (barometers) measure gas pressure directly. Barometers are used to measure atmospheric pressure.

Factors that affect gas pressure:

1. amount of gas (in moles)2. volume (in mL, cm3, L)3. temperature (°C, K)

The relationship between these factors can be expressed with gas laws.

Jan 8­6:52 AM

Boyle’s Law: As the pressure on a gas increases the volume decreases (if the temperature remains constant).

Formula: P1V1 = P2V2

If the volume of a gas is 5.0L when the pressure on it is 758 torr, what must the pressure be to change the volume to 3.5L?

If 4.41 dm3 of N2 is collected at a pressure of 94.2 kPa, what will the volume be for this gas at STP?

Jan 8­6:52 AM

Charles’ Law: If you heat a gas, it expands. As the temperature increases the volume increases (if pressure remains constant).

Formula: V1/T1 = V2/T2

******** ALL TEMPERATURES MUST BE IN KELVIN!!********

With a constant pressure, the volume of a gas is increased from 15.0 L to 32.0 L. If the new temperature is 20°C, what was the original temperature?

Jan 8­7:11 AM

Extra credit: Film this and upload, email or bring on flash drive to show.

Real life application of Charles' Law:Coke Can­Fill a coke can with a small amount of water, as you heat the water inside to near boiling, immediately invert the coke can into ice­cold water so the coke can is experiencing a dramatic drop in temperature, volume of can will decrease (can will crush in on itself). (look up examples on youtube) Due on Monday, Decemeber 2!

Jan 8­6:53 AM

Gay­Lussac’s Law: As the temperature of an enclosed gas

increases, the pressure also increases (volume stays constant).

Formula: P1/T1 = P2/T2

The pressure in a tire is 1.8 atm at 20°C. After a 200 mile trip, the pressure reading for the tire 1.9 atm. What is the temperature inside the tire at that new pressure?

Unit 13 notes.notebook

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December 03, 2013

Jan 8­6:54 AM

Combined Gas Law: combines Boyle's, Charles', and

Gay­Lussac's.

Formula: P1V1 = P2V2T1 T2

Ideal Gas Law: modified version of the combined gas law that also

includes: number of moles and ideal gas constant.

Formula: PV =nRT

All volumes must be in liters.

All temperatures must be in Kelvin.

Match R to correct pressure units.

“n” must be in moles.

Jan 8­7:09 AM

What is the pressure in atm exerted by 0.5 moles of N2 in a 10 L container at 298K?

What is the volume of 0.250 moles of O2 at 20°C and 0.974 atm?

Jan 8­7:10 AM

What is the temperature of 76 g of Cl2 in a 24 L container at 890 mmHg?

A deep underground cavern contains 2.24 x 106 L of CH4 at a pressure of 1.50 x 103 kPa and a temperature of 315K. How many kilograms of CH4 does the cavern contain?

Nov 25­8:27 AM

Stoichiometry of Gases

Volume­Volume (22.4 L = 1 mole of anything at STP)

a. What volume of O2 is required for combustion of 0.35 L of C3H8?

i. Balanced equation

ii.Proportion (Given/coefficient = unknown/coefficient)

iii. Solve!

b. What volume of NaCl at STP is produced if 25.0 g of Na is reacted with an excess of Cl2?

Jan 8­7:10 AM

An ideal gas follows the gas laws at all pressures and temperatures. They don’t really exist!!

Real gases condense into liquids at low temperatures and high pressures of the individual gases.

Most gases behave ideally when their particles are far enough apart and have enough kinetic energy. Real gases deviate because the particles occupy space and exert attractive forces on each other. Non­polar and monatomic gases behave more ideally (Noble gases, N2, H2).

The real gases that do not behave ideally are highly polar (NH3, H2O).

Jan 8­7:11 AM

Dalton’s Law: in a mixture of gases, the total pressure is the

sum of the partial pressures of the individual gases.

Formula: P total = P1 + P2 + P3.....

In a container there are 4 gases with the following pressures: Gas 1­­2.5 atm, Gas 2­­1.9 atm, Gas 3­­798 mmHg, Gas 4­­2.1 atm. Find the total pressure in the container.

In a sample of HCl gas, the pressure of the gas is found to 0.87 atm. If hydrogen makes up 34% of the gas, what is the pressure of the hydrogen? What is the pressure of the chlorine?

Unit 13 notes.notebook

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December 03, 2013

Dec 2­8:48 AM

Gases Collected by Water Displacement:Formula: Patm = Pgas + PH2O

Oxygen gas from the decomposition of potassium chlorate, KClO3, was collected by water displacement. The barometric pressure and temperature during the experiment were 731.0 torr and 20.0 C, respectively. What was the partial pressure of the oxygen collected?

Jan 8­7:13 AM

Graham’s Law: gases of lower mass diffuse and effuse faster than heavier gases.

Diffusion: gas particles move from areas of high concentration to areas of low concentration until equal

Effusion: gas particles escape through tiny holes in a container

Formula: rate A/rate B = square root(molar massB)/sq.rt(molar massA)

If CO2­ has a speed of 22 m/s at 20°C, what is the speed of HCl at the same temperature?

What is the ratio of the speeds of helium compared to oxygen?