Changes of state

solid

• molecules packed tightly in a regular structure.

• vibrate around a fixed position.

• atoms held together by strong attractive forces.

liquid

• molecules close together BUT they can move

• particles in a liquid can flow and change shape, to fill the shape of the container.

• difficult to compress a liquid (because the particles are close together.)

gas

• molecules far apart - fast, random movement

• weak attractive forces between molecules.

• gas can be compressed

• gas can fill the shape of any container

solid → liquid

melting

• particles gain kinetic energy from heat.

• energy breaks strong intermolecular bonds.

• internal energy of the system increases

liquid → gas

evaporation/boiling

• internal energy of the system increases

gas → liquid

condensation

• lower temperatures = particles have less kinetic energy.

• bonds from between particles

• internal energy of the system decreases

liquid → solid

solidification/freezing

• lower temperatures = particles have less kinetic energy.

• bonds from between particles

• internal energy of the system decreases

solid → gas

sublimation

• internal energy of the system increases

explain the process of evaporation

particles can can evaporate from a liquid’s surface below the liquids boiling point.

Particles can evaporate if:

1. travelling in the correct direction (to escape the liquid)

2. particles travelling fast enough (have enough kinetic energy) in order to overcome the attractive forces of the other liquid particles.

specific heat capacity

‘the energy required to change the temperature of an object by one degree Celsius per kilogram of mass’

J/Kg degrees Celsius

when the temperature of a system is increased by supplying energy to it, the increase in temperature depends on:

• the mass of the substance heated.

• what the substance is made of.

• the energy put into the system.

equation for specific heat capacity

specific heat capacity =

energy transferred/mass x temp.change

equation for energy transferred/thermal energy

thermal energy =

mass x specific heat capacity x change in temp.

describe an experiment to obtain a temperature-time graph, to show constant temperature during a change of state

1. fill beaker with 150ml water and put on tripod and gauze

2. put test tube of stearic acid into clamp supported by a retort stand.

3. heat water over Bunsen flame, and bring to the boil.

4. put test tube of stearic acid into the water.

5. put thermometer into stearic acid until it reaches 100 degrees Celsius.

6. move stearic acid back to retort stand

7. record temp. every minute until acid reaches 50.

8. plot temperature-time graph.

specific heat capacity of water

4200 J/Kg degrees Celsius

Describe an experiment to investigate the specific heat capacity of water and solids

1. Place the beaker on the digital balance and set to zero.

2. Add approx. 250 ml of water and record the mass of the water.

3. Place the immersion heater and thermometer in the water.

4. Connect the circuit :

   • ammeter in series with power supply and immersion heater.

   • voltmeter in parallel with the immersion heater

5. Record the initial temperature of the water at 0 seconds

6. Turn on the power supply, set it at approximately 10 V, and start stopwatch

7. Record the voltage from the voltmeter and the current from the ammeter

8. Continue to record the temperature, voltage and current every 60 seconds for 10 minutes

9. Repeat experiment, replacing the beaker of water for the solid block of aluminium.

explain how a vacuum reduces thermal energy transfer

• there are no atoms/molecules/particles in a vacuum.

• no conduction takes place.

• no convection currents are created.

what is Brownian motion?

the random movement of particles in a medium (gas or liquid) produced by large numbers of collisions with smaller particles (which are often too small to see.)