Physics - 6 Molecules and Matter - 6.5 Specific Latent heat & 6.6 Gas Pressure and Temperature & 6.7 Gas Pressure and Volume

Pressure and volume

Latent heat of fusion

energy required to change the state of 1 kg of a substance from solid to liquid

Specific latent heat is measured in...

J/kg

Specific latent heat of fusion =

energy ÷ mass

Lf =

E ÷ m

How do you measure the Lf of ice? [3]

- fill a funnel with ice chips and suspend it over a beaker/measuring cylinder
- use a low-voltage heater attached to a joulemeter to melt the ice
- use the measurement of the mass and of the energy supplied to find the Lf

Latent heat of vaporisation

energy required to change the state of 1 kg of a substance from liquid to gas

Specific latent heat of vaporisation =

energy ÷ mass

Lv =

E ÷ m

What causes gas pressure?

collision of gas molecules with the sides of their container

Why does temperature increase gas pressure?

the particles have more kinetic energy, so they move faster, so they make collisions more often and with more force with the container

Gas pressure and temperature experiment

use dry air in a water bath attached to a pressure gauge to observe the effect of rising temperature

Smoke cell

a small glass cell filled with smoke

Random motion

movement in all directions and at different speeds

Observing random motion [4]

1. a small glass cell is filled with smoke
2. light is shone through it
3. smoke is viewed through a microscope
4. see the smoke particles moving a changing direction

What do we see in the smoke cell?

air particles hitting the smoke and influencing its direction

Pressure produces a net force at right angles to the...

wall of the container of the gas

Why do we compress gas slowly?

otherwise, the work done would increase the internal energy store of the gas and its temperature

Investigating pressure and volume experiment

slowly increase the pressure and observe the effect it has on the volume

Boyle's law

pressure x volume is constant for a fixed mass of gas at a constant temperature

Why does pressure increase as volume decreases? [3]

- the number of gas molecules is constant
- if the space is reduced, the particles don't travel as far between each impact with the container
- the molecules hit the surface more often, so the impacts per unit of space increase

Pressure is measured in...

Pascals (Pa) or N/m²

Pressure is ... to volume of gas

inversely proportional

(BL, w) constant =

pressure x volume

(BL, s) constant =

pV