Gas laws

Question 1

What is Boyles law?

Give an simple example.

Answer 1

At a constant temperature, volume is inversely proportional with absolute pressure.

Example: occlude a syringe of air. The further you depress the syringe, the harder it gets as the small volume creates higher pressure.

Question 2

Explain why Boyles law occurs?

Answer 2

The constant temperature means there is a constant energy of motion. However the smaller volume brings particles closer together, meaning there are more collisions and more pressure.

Question 3

What is the equation for Boyles law?

Answer 3

V 🐟 1/p (fish = little proportional squiggle sign)

Or

PV = K1 (K is a constant)

(YouTube)

Question 4

According to Boyles law, what happens if we half the volume?

Answer 4

We double the pressure

Question 5

A 10L cylinder has a pressure of 137 bar, how much available O2 is left?

Answer 5

Boyles law:

V 🐟 1/P
Or P1 x V1 = P2 x V2

137 bar = 13700kPa
Absolute pressure = 13800

13800 x 10 = 100 kPa x V2
V2 x 100 kPa = 138000
V2 = 1380
10L will remain in the cylinder so 1370L are available.

Question 6

What is Charles law?

Example.

Answer 6

At a constant pressure, volume varies directly with temperature

Heat the gas in a hot air balloon and it expands

Question 7

What is the formula for Charles law?

Answer 7

V 🐟 T (Kelvins)

Or

V/T = K2 (constant)

Question 8

If you heat a syringe attached to a pressure gauge, what gas law best describes; a syringe with a free plunger and a syringe with a fixed plunger?

Answer 8

Free = Charles
Fixed = third (Gay-Lussac’s)

Question 9

What is the third gas law?

Example?

Answer 9

(Gay-Lussacs)

At a constant volume, absolute pressure is proportional to absolute temperature.

Heating a deodorant can

Question 10

What is the equation for the third gas law?

Answer 10

P 🐟 T or P/T = K3 (constant)

Question 11

What is the combined gas law?

Answer 11

All gas laws = constants, therefore:

PV/T = constant

Or:

P1V1/T1 = P2V2/T2

Temperature must be in Kelvin, the other units can be anything.

Question 12

What is Avogadro’s principle?

Answer 12

That equal volumes of gasses at the same temperature and pressure will have the same number of molecules

(YouTube)

Question 13

What is avogadros constant?

Answer 13

1 mole = 6.022 x 10 (power of 23)

Question 14

According to avogadros principle, what volume does one mole of gas occupy at standard temperature and standard pressure?

Answer 14

22.4L

Standard temp = 273.15 K and pressure = 1 atm

Question 15

What is the ideal gas law?

Answer 15

PV/T =nR

Or

PV = nRT

Question 16

How is the ideal gas law derived?

Answer 16

PV/T = constant.

The constant is only for a fixed gas quantity, therefore the value of the constant varies with the number of moles (n). And the universal gas constant = R

PV/T = nR

Question 17

What is the value of the universal gas constant?

Answer 17

R = 8.31 JK-1mol-1

Question 18

A full N2O cylinder has 3.4kg of nitrous, how much can you get out?

Answer 18

Molecular weight = 44, therefore 1 mole of N2O = 44g

3400/44 = 77.2

77.2 x 22.4 (L) = 1730L (-whatever residual volume of size of cylinder)

Question 19

What is Dalton’s law?

Answer 19

In a gas mix, the pressure exerted by each gas is the same as if the gas was there alone.

P (total) = P1 + P2 + P3…..

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Question 20

How do we fit Dalton’s law into the ideal gas law?

Answer 20

PV = (n1 + n2…..)RT

Question 21

If an oxygen cylinder has a pressure of 100kPa with 20.9% O2 and 79%N, how much pressure does each gas exert?

Answer 21

O2 = 20.9 kPa and N = 79kPa