Chemistry - Gas Laws

Pressure

-force per unit area on a surface area (P = F/a)

-For gases: the pressure of the gas is directly related to the FORCE of the gas particles colliding with the sides of the container, it is INDIRECTLY proportional to the area of the container (sides)

How do you INCREASE force or decrease area? (increase P)

-Increase T

-Decrease V

-Add more gas particles (more gas particles colliding with the sides)

Gases move from areas of ____ pressure to ____ pressure continuously and spontaneously

HIGH to LOW

Barometer

-Measures atmospheric pressure

Manometer

-Measures pressure in a CLOSED container

1 atm = …..

-760 mm Hg

-760 torr

-101.325 kPa

Standard Temperature

-0 degrees C

-273.15 K (CONVERT ALL TEMPERATURES TO KELVIN FOR CALCULATIONS)

Standard Pressure

1 atmosphere

Why does a container have a periodic fast and slow flow when pouring water?

-Small gaps allow gas outside (high pressure) to get to the inside to get to the area with lower pressure (remember for the gas in the container as V increases, P decreases)

What is a vacuum?

Empty space, no air, no gas, no liquid, no solid, NOTHING

How does a mercury barometer make a vacuum?

1. First, the tube is filled with mercury and turned upside down into the dish. Some mercury stays in the tube, and some flows out into the dish.

2. When air pushes down on the mercury in the dish, it pushes the mercury up the tube. This creates a vacuum at the top of the tube, as there is no mercury present.

3. The higher the mercury goes in the tube, the stronger the air pressure is.

4. If the air pressure gets lower, the mercury in the tube goes down.

Because the tube’s top end is closed and no air enters when it’s inverted, the space above the mercury column has essentially no air in it. This empty top region is a (near) vacuum – often called the Torricellian vacuum

Why does suction technically not exist in suction cups?

When pressing down on a suction cup, air beneath it is forced out, creating an area with lower pressure beneath the cup. The pressure outside the cup is higher and therefore pushes down on the suction cup, causing it to adhere to the surface that it is on

Why does suction technically not exist in a vacuum cleaner?

Vacuum cleaners have to create low pressure

→ Uses a fan to move air faster, creating low pressure in front of the fan blade from the air in the back

→ Hose of a vacuum cleaner allows air with high pressure to move inside to get to low pressure

→ THINGS GET PUSHED IN TO CLEANER, NOT SUCKED UP (high pressure air is pushed, bringing anything with it that is in the way)

Why does suction technically not exist in a drinking straw?

-When breathing in, you expand your diagphragam (lungs expand = volume goes up, pressure goes down)

→ High pressure wants to get to the lower pressure in your body (as liquid goes up a straw, it means gas with high pressure is trying to push it up)

Boyle’s Law

For a fixed quantity of gas at CONSTANT T, Pressure varies INVERSELY with volume.

P1V1 = P2V2 = k

Charles’ Law

For a fixed quantity of gas at CONSTANT P, Volume varies DIRECTLY with Temperature (IN KELVIN)

V1/T1 = V2/T2 = k

Gay-Lussac’s Law

For a fixed quantity of gas at CONSTANT V, Pressure varies DIRECTLY with Temperature (IN KELVIN)

P1/T1 = P2/T2 = k

Combined Gas Law

For a fixed quantity of gas, Pressure and Temperature (IN KELVIN) vary directly and indirectly with volume

P1V1/T1 = P2V2/T2 = k

Dalton’s Law of Partial Pressures

The total pressure of a mixture of gases is equal to the sum of the partial pressures of each gas

Total pressure = P1 + P2 + P3 + …

(Each gas does NOT know the other one exists, therefore adding a gas only changes the TOTAL pressure, not the pressure of other gases in the mixture)

Collecting Gases by Water Displacement

-If a gas is bubbled into an inverted container full of water, the gas will move to the top and push out water. However, the gas in the container is a MIXTURE of the displacing gas and WATER VAPOR.

Inside → Total pressure = Pgas - PH2O

Ideal Gas Law

PV = nRT

P = pressure

V = volume

n = # of moles

(ideal gas constant) R = 0.0821 L atm / mol K or 62.4 L mm Hg / mol K

T = temperature in KELVIN

Avogadro’s Law

-Equal volumes of gases at the same T and P contain equal numbers of molecules

22.4 L of any gas at STP = 6.022 × 10²³ particles = 1 mole

V1/n1 = V2/n2

Graham’s Law of Effusion

Velocity (rate) is indirectly proportional to time

Va/Vb = tb / ta = (MMb / MMa)^1/2