Chapter 4- Gases

Question 1

Pressure

Answer 1

Force per unit are

Question 2

The SI unit for pressure. What does it represent?

Answer 2

Pascals (Pa). Represents a force of 1N on an area of 1m^2

Question 3

Atmospheric pressure

Answer 3

The force per unit area exerted by air on all objects. At sea level the average is 101kPa

Question 4

Standard temperature and pressure (STP)

Answer 4

0 degrees C, 101.325 kPa (1 atm)

Question 5

Standard ambient temperature and pressure (SATP)

Answer 5

25 degrees C, 100 kPa, closer to lab conditions than STP

Question 6

What did Evangelista Torricelli invent?

Answer 6

Accidently invented new way of measuring atmospheric pressure- mercury barometer.

Question 7

Boyle’s Law

Answer 7

As the pressure on a gas increases, the volume will decrease proportionally, provided the temperature and chemical amount of the gas remain constant.

Question 8

Absolute zero

Answer 8

-273 degrees Celsius, the lowest possible temperature. Kelvin scale based on absolute zero -273 degrees C = 0K

Question 9

Charles’ Law

Answer 9

As the temperature of a gas increases, the volume increases proportionally, provided that pressure and chemical amount remain constant

Question 10

The Combined Gas Law

Answer 10

The product of the pressure and volume of a gas is proportional to its temperature in kelvin

Question 11

What does the kinetic molecular theory explain about the properties of gases?

Answer 11

• gases are compressible because the large distance between molecules allows them to be forced together
• Gas pressure is the result of gas molecules colliding with objects so the pressure is the total force of these collisions distributed over an area of the container wall
• Boyle’s Law. If volume is reduced, molecules move a shorter distance before colliding with the container wall, they will collide more frequently which will increase pressure.
• Charles’ Law. Increase in temperature means increase in kinetic energy therefore speed of entities. In a container where pressure is kept constant, the molecules will collide with more force, increasing the volume.

Question 12

Law of Combining Volumes

Answer 12

When measured at the same temperature and pressure, volumes of gaseous reactants and products of chemical reactions are always in simple ratios of whole numbers.

Question 13

Avogadro’s Theory

Answer 13

Equal volumes of gases at the same temperature and pressure contain equal numbers of molecules.

Question 14

Molar Volume

Answer 14

The volume one mole of gas occupies at a specific temperature and pressure. Same for all gasses at the same temp and pressure SATP- 24.8L/mol STP- 22.4L/mol

Question 15

Ideal Gas

Answer 15

A hypothetical gas that obeys all gas laws perfectly under all conditions.

Question 16

Boyle’s Law Formula

Answer 16

P1V1 = P2V2

P = Pressure (kPa)
V = Volume (L)

Question 17

Charles’ Law Formula

Answer 17

V1/ T1 = V2/ T2

V = Volume (L)
T = Absolute Temperature

Question 18

Convert 100kPa to atm and mmHg

Answer 18

1 atm = 101.325 kPa 100/ 101.325 = 0.987

760 mmHg = 1 atm 760 x 0.987 = 750 mmHg

Question 19

To convert Celsius to Kelvin

Answer 19

Add 273

Question 20

Combined gas law formula

Answer 20

P1V1 / T1 = P2V2/T2

P = pressure (kPa)
V = Volume (L)
T = Absolute temperature

Question 21

Steps to predicting volume using law of combining volumes

Answer 21

• Write out balanced chemical equation and given volume
• How many moles of one substance reacts with moles of another substance- ratio of moles will be the same as ratio of volume
• multiply/ divide volume by a factor of the ratio

Question 22

Formula for Molar volume

Answer 22

V = nVm 
Volume = chemical amount (moles) x Molar volume

Question 23

Ideal gas law formula

Answer 23

PV = nRT

Pressure x volume = chemical amount (moles) x universal gas constant ( 8.314) x absolute temperature

Question 24

How to find the universal gas constant

Answer 24

Substitute STP or SATP conditions into the ideal gas law and solving for R

Question 25

Molar volume of a gas at SATP

Answer 25

24.8 L/mol

Question 26

Molar Volume of a gas at STP

Answer 26

22.4 L/mol