5c: Change of state

3 states of matter

solid, liquid, gas

solid

definite shape and volume

solid - particle arrangement

- closely packed
- vibrate about fixed positions

liquid

- indefinite shape
- definite volume

liquid - particle arrangement

- closely packed
- flow over one another

gases

indefinite shape and volume

gases - particle arrangement

- far apart
- move randomly

why are gases highly compressible

- large gaps between particles
- easier to push particles closer together

are changes of state reversible

yes

change of state

- number of molecules and mass doesn't change
- energy changes

changes of state

- melting
- boiling
- condensing
- freezing
- subliming

melting

solid to liquid

boiling

liquid to gas

condensing

gas to liquid

freezing

liquid to solid

subliming

solid to gas

heating a system

- increased kinetic energy
- temperature increases
- change of state

factors affecting increase in system temperature

- mass
- type of material
- amount of energy (thermal)

specific heat capacity

amount of energy required to raise the temperature of 1 kg of the substance by 1 C

substance with a low specific heat capacity

heats up and cools down quickly (less energy required)

substance with a high specific heat capacity

heats up and cools down slowly (more energy required)

formula for change in thermal energy

mass x specific heat capacity x change in temperature

investigating changes of state - aim

investigate how the temperature of ice varies when it changes state from a solid to a liquid

investigating changes of state - equipment

- thermometer
- ice cubes
- beaker
- tripod and gauze
- bunsen burner
- stopwatch

investigating changes of state - method

- place ice cubes and thermometer in beaker
- place beaker on tripod and gauze
- heat beaker
- take regular temperature measurements

investigating changes of state - systematic errors

eye level to avoid parallax errors

investigating changes of state - random errors

- begin experiment when temp is below 0
- enough ice cubes to surround the thermometer

investigating changes of state - safety considerations

- wear goggles
- bunsen burner on heat proof mat
- react to spills

investigating changes of state - graph

investigating specific heat capacity - aim

determine the specific heat capacity of a solid and of water by measuring the energy required to increase the temperature of a known amount by one degree

investigating specific heat capacity - apparatus

- thermometer
- block of aluminium
- beaker of water
- immersion heater
- voltmeter
- ammeter
- power supply
- digital balance
- stopwatch

investigating specific heat capacity - method

- place beaker on digital balance
- add 250ml water and record mass
- place immersion heater and thermometer in water
- connect up circuit
- record initial temperature at 0 s
- turn on power supply and start stopwatch
- record voltage and current every 60 secibds
- repeat but replace beaker of water with solid block of aluminium

investigating specific heat capacity - analysis

- energy = current x voltage x time
- ΔQ = m x c x ΔT

investigating specific heat capacity - systematic errors

- digital balance set to 0
- water lost to surroundings
- gradient on straight-line region

investigating specific heat capacity - random errors

- stir constantly with thermometer
- choose higher value if they change constantly

investigating specific heat capacity - safety considerations

- use a heatproof mat as immersion heater is hot
- immersion heater connected to DC supply
- use clamp stand to hold beaker
- wear goggles
- react quickly to spills

investigating specific heat capacity - graph