Gas Laws

Question 1

Define a mole of a substance

Answer 1

A mole has as many particles as 12g of carbon-12

Question 2

What is avogadros law?

Answer 2

It states that equal volumes of gases contain the equal number of molecules under equal conditions of temperature and pressure

Question 3

What does Charles law state?

Answer 3

At constant pressure, the volume and temperature of a fixed mass of a gas are directly proportional to eachother

Question 4

What does Boyle’s law state?

Answer 4

At a constant temperature, the volume and pressure of a fixed mass of a gas is inversely proportional

Question 5

Give the formula for the law of combining volumes

Answer 5

P1V1 P2V2

T1 = T2

Question 6

What is standard pressure and temperature

Answer 6

Temp - 273K

Pressure - 1 x 10^5 pascals

Question 7

State gay-lussac’s law

Answer 7

When gases react, the volumes of the reacting gases and any gaseous products bear a simple whole number ratio when volumes are measured at the same temperatures and pressure

Question 8

Explain how avogadro’s law provides an explanation for gay-lussac’s law

Answer 8

Avogadros law explained gay-lussac’s law of combining volumes in whole numbered ratios more in terms of combining of actual molecules of reacting gases and still kept the pressure and temperature constant

Question 9

What is an ideal gas?

Answer 9

Obeys all Gas laws and the kinetic theory of gases at all temperatures and pressures

Question 10

Give one reason why real gases differ from ideal gases

Answer 10

Molecules of gases are often attracted weakly to each other

collisions not actually elastic, collide with eachother and often lose or gain energy

Question 11

Explain the kinetic theory of gases

Answer 11

Collisions in gases are always elastic [no reaction ever occurs]
No attraction or repulsions
Take up such a small volume

Question 12

When are gases closest to ideal behaviour?

Answer 12

High temperature

Low pressure

Question 13

How to find out which gas is closest to an ideal gas

Answer 13

Covalent
Single bonds
Low Mr

Question 14

What is the equation of state for an ideal gas?

Answer 14

PV = nRT
pressure - Pascals [x1000 from kPascals]
volume - m3 [cm - x 10^-6]
n - moles
r - give
t - +273

Question 15

How many moles of gas are present in a sample containing 1.8 x10^23 atoms of chlorine at stp

Answer 15

1.8 x 10^23 / 2 = 9 x10^23 / 6 x 10^23 = 1.5 moles

Question 16

i) Carbon dioxide is stored under pressure in liquid form in a fire extinguisher. Two kilograms of carbon dioxide are released into the air as a gas on the discharge of the fire extinguisher. What volume does this gas occupy at a pressure of 1.01 x 10^5 Pa and a temperature of 290K
ii) What mass of helium gas would occupy the same volume at the same temperature and pressure?

Answer 16

i) 2000 g (2 kg) / mr (44) = 45.5 MOLES
PV = nRT
V = nRT
         P
45.5 x 8.3 x 290 
    1.01 x 105
1.069 – 1.10 
ii) 45.5 x 4 (mr) = 182 g

Question 17

Give one reason why carbon dioxide is more easily liquified than helium

Answer 17

Stronger intermolecular forces

Question 18

A foil balloon has a capacity of 10 litres. How many atoms of helium occupy this balloon when is filled with 10% v/v mixture of helium in air at room temp and pressure

Answer 18

10l         1
100l =   10
1 l in 10 lr balloon
1 / room temp = 24 = .0416 moles 
.0416 x 6 x 10^23 = 2.4 x 10^22

Question 19

A small quantity of the volatile organic solvent propanone evaporates at room temperature and pressure. Use the equation of state for an ideal gas to calculate the volume, in litres, of propanone vapour formed when .29g of liquid propanone evaporates taking room temperature as 20 degrees celcius and room pressure as 101kPa

Answer 19

PV = nRT => V = nRT 
T = 20 + 273 = 293 K
Pa -101 x 1000 = 1.01 x 105 Pa
n = 0.29 /58 = 0.005 mol 
 V = 0.005 x 8.3 x 293 (3) = 0.00012 m3
                 1.01 x 105
0.00012 x 1000 = 0.12 litres