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GAS LAWS

I. States of Matter

A. Solid: state in which matter holds a definite shape and volume. The particles are closely packed together and held rigidly in place. The particles have a very strong attraction to each other. Solids are considered to be a compressed state of matter (the particles cannot be pushed closer together.)

B. Liquid: state in which matter does not hold a definite shape but occupies a definite volume. The particles are still very close together, but have the freedom to change places or “flow” past each other. The particles have strong attractions to each other, but not as strong as solids. Liquids are considered to be a compressed state of matter.

C. Gas: state in which matter has no definite shape or volume. The volume of the container is the volume of the gas sample. The particles are very far apart (relatively speaking) and have little or no attraction for each other. The particles are in constant, random motion. Different gases can move through each other rapidly in a process called diffusion. Gases are matter so they do have mass. Gases exert pressure through collisions between the gas particles and their container. The pressure is dependent on the temperature of the gas. The representative particles of a gas may be atoms (He, Ne, Ra) or molecules (O2, CO2, CH4, N2, H2). Gases are easily compressed (the particles can be pushed closer together).

D. Plasma: fourth state of matter, ionized gases. Example: interior of the sun

II. Measuring Gases – In order to describe a gas sample completely and then make predictions about the behavior under changed conditions, it is important to deal with the values of four variables: amount of substance (moles), volume, temperature, and pressure.

A. Amount of substance (n) – the quantity of a given gas sample is expressed in terms of moles of gas. It can also be related to the number of particles present.

B. Volume (V) – the space occupied by matter

1. A gas will uniformly fill any container in which it is placed; the volume of a sample of gas is equal to the volume of the container.

2. Typical volume conversions: 1 L = 1000 mL = 1000 cm3

C. Temperature (T) – the average kinetic energy of the particles of a substance.

1. Fahrenheit (°F) – scale of temperature commonly used in the U.S.

2. Celsius (°C) – scale of temperature that is more compatible with the metric system.

3. Kelvin (K) – scale of temperature that is the SI standard.

a. No degree sign (°) is used with Kelvin temperatures.

b. There are no negative temperatures on the Kelvin scale.

c. One degree of Kelvin temperature is equal to one degree of Celsius temperature.

d. Absolute zero or 0K is the point at which all motion stops.

e. All calculations involving gases should be made using the Kelvin scale.

4. Typical temperature conversions:

a. °F = (1.8 ( °C) + 32

b. °0 C = 273 K (be able to find this on formula chart)

D. Pressure – force per unit area; the collisions of gas particles with the container walls exerts an outward push or force on the wall (if a space or volume is lacking measurable gas pressure it is called a vacuum – it is lacking matter).

1. Units of gas pressure – atmospheres (atm), mm Hg or torr, pascals, and kilopascals

2. Typical pressure conversions: 1 atm = 760 mm Hg (torr) = 101.3 kPa (Be able to find this on formula chart)

3. Barometers – instruments used to measure atmospheric pressure

4. Manometer – instrument used measure the pressure of a gas in a closed container; similar to a barometer; example: blood pressure cuff

Standard pressure at sea level is 1 atm and Standard temperature 0°C or 273 K (MEMORIZE this)

Dalton’s Law – the total pressure of a mixture of gases is the sum of the individual or partial pressures of all the gases mixed together.

A. Formula: Ptotal = Pa + Pb + Pc………….

Example: A metal tank contains three gases: oxygen, helium, and nitrogen. If the partial pressures of the three gases in the tank are 35 atm of O2, 5 atm of N2, and 25 atm of He, what is the total pressure inside of the tank?

Boyle’s Law: when the temperature and the number of moles of a sample of gas are held constant, its volume is inversely proportional to the pressure applied.

A. Inverse (or indirect relationship) – volume will increase with a decrease in pressure, volume will decrease with an increase in pressure.

B. Formula: P1 ( V1 = P2 ( V2

C. Units: Volume and Pressure may be in any units as long as you are consistent.

Example: 50.0 mL of a gas has a pressure of 740. mm Hg when it is in a container. What would the volume of the gas be if it was at standard pressure?

HOMEWORK: DATLON'S and BOYLE'S

1. Blast furnaces give off many unpleasant and unhealthy gases. If the total air pressure is 0.99 atm, the partial pressure of carbon dioxide is 0.050 atm, and the partial pressure of hydrogen sulfide is 0.020 atm, what is the partial pressure of the remaining air?

2) In a thermonuclear device, the pressure of 0.050 liters of gas within the bomb casing reaches 4.0 x 106 atm. When the bomb casing is destroyed by the explosion, the gas is released into the atmosphere where it reaches a pressure of 1.00 atm. What is the volume of the gas after the explosion?

3) Synthetic diamonds can be manufactured at pressures of 6.00 x 104 atm. If we took 2.00 liters of gas at 1.00 atm and compressed it to a pressure of 6.00 x 104 atm, what would the volume of that gas be?

4) The highest pressure ever produced in a laboratory setting was about 2.0 x 106 atm. If we have a 1.0 x 10-5 liter sample of a gas at that pressure, then release the pressure until it is equal to 0.275 atm, what would the new volume of that gas be?

5) If a mixture of gases contains 4.5 atm of O2 and 785 mm Hg of N2. What is the total pressure of the mixture?

Charle’s Law – when the pressure and amount of a gas are held constant, the volume of the gas is directly proportional to its KELVIN temperature.

A. Direct relationship – the volume will increase if the Kelvin temperature is increased; the volume will decrease if the Kelvin temperature is decreased.

B: Formula [pic]

C. Units – REMEMBER: 1 cm3 = 1 mL and 1000 mL = 1 L. Temperature must be in KELVIN.

Example: At 20°C, the volume of a gas is 100. mL. What would the volume of the gas be 100°C?

Gay – Lussac’s Law: when the volume and number of moles of a sample of gas are held constant, its pressure is directly proportional to the KELVIN temperature.

A. Direct relationship – the pressure will increase if the Kelvin temperature is increased; the pressure will decrease if the Kelvin temperature is decreased

B. Formula: [pic]

C. Units: Pressure can be in any units (as long as you are consistent, but TEMPERATURE MUST BE IN KELVIN!!!!!

Example : The pressure of a tank of gas is 2.0 atm, and the temperature is 40°C. If the volume remains constant, what will the new pressure be if the temperature is lowered to 20°C?

HOMEWORK: CHARLES' and GAY-LUSSAC'S

1) The temperature inside my refrigerator is about 40 Celsius. If I place a balloon in my fridge that initially has a temperature of 220 C and a volume of 0.50 liters, what will be the volume of the balloon when it is fully cooled by my refrigerator?

2) A man heats a balloon in the oven. If the balloon initially has a volume of 0.4 liters and a temperature of 20 0C, what will the volume of the balloon be after he heats it to a temperature of 250 0C?

3) On hot days, you may have noticed that potato chip bags seem to “inflate”, even though they have not been opened. If I have a 250 mL bag at a temperature of 19 0C, and I leave it in my car which has a temperature of 600 C, what will the new volume of the bag be?

4) A soda bottle is flexible enough that the volume of the bottle can change even without opening it. If you have an empty soda bottle (volume of 2.0 L) at room temperature (25 0C), what will the new volume be if you put it in your freezer (-4 0C)?

5) Determine the pressure change when a constant volume of gas at 1.00 atm is heated from 20.0 °C to 30.0 °C.

6) A gas has a pressure of 0.370 atm at 50.0 °C. What is the pressure at standard temperature?

7) A gas has a pressure of 699.0 mm Hg at 40.0 °C. What is the temperature at standard pressure?

8) If a gas is cooled from 323.0 K to 273.15 K and the volume is kept constant what final pressure would result if the original pressure was 750.0 mm Hg?

Avogadro’s Principle – if there are equal volumes of gases at equal pressures and temperatures, then each sample has an equal number of particles (moles)

A. Direct relationship – the volume will increase if the number of moles (n) is increased, the volume will decrease if the number of moles decreases.

B. Formula: [pic]

C. Units: volume can be in any units; typically we will use L or mL. “n” refers to the number of moles – it can refer to the number of particles but not grams!

Example : A balloon with a volume of 4.00 L is known to contain 0.200 moles of gas. How many moles of gas remain if some of the gas is released and the new volume is 3.25 L. Assume temperature and pressure remains constant.

The Combined Gas Law – Boyle’s, Charles’, and Gay-Lussac’s Laws combined.

A. Formula: [pic]

B. Units – any units for volume and pressure can be used as long as you are consistent, BUT YOUR TEMPERATURE MUST BE IN KELVIN!

D. Examples: Show all work including units.

1. A sample of gas has a volume of 1.25 L at 25°C and 0.876 atm. What is the new volume when the temperature decreases to 15°C and the pressure decreases to 0.750 atm?

2. A sample of gas occupies 15.0 L at 22. °C and 754 mm Hg. If the volume increases to 23.0 L and the pressure decreases to 723 mm Hg, what is the new temperature?

HOMEWORK: AVOGADRO'S and COMBINED

1) A balloon with a volume of 8.00 L is known to contain 1.200 moles of gas. How many moles of gas remain if some of the gas is released and the new volume is 5.25 L. Assume temperature and pressure remain constant.

2) A container originally contains 34 moles of oxygen gas at a volume of 2.4 L. If the container has 12 more grams of oxygen gas pumped into it, what will be in the new volume of the container. Assume constant temperature and pressure.

3) If I initially have a gas at a pressure of 12 atm, a volume of 23 liters, and a temperature of 200 K, and then I raise the pressure to 14 atm and increase the temperature to 300 K, what is the new volume of the gas?

4) A gas takes up a volume of 17 liters, has a pressure of 2.3 atm, and a temperature of 299 K. If I raise the temperature to 350 K and lower the pressure to 1.5 atm, what is the new volume of the gas?

5) A gas that has a volume of 28 liters, a temperature of 45 0C, and an unknown pressure has its volume increased to 34 liters and its temperature decreased to 35 0C. If I measure the pressure after the change to be 2.0 atm, what was the original pressure of the gas?

6) A gas has a temperature of 14 0C, and a volume of 4.5 liters. If the temperature is raised to 29 0C and the pressure is not changed, what is the new volume of the gas?

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