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