Chemistry calorimetry notes
Enthalpy change
When experiencing the same change of heat energy, a material with a greater mass will
increase in temperature less than the material with the lesser mass
Water has a specific heat capacity of 4.2J
SHC (J/K/G)- the amount of heat energy it takes to raise 1g of a substance by 1k
When calculating SHC, mass and specific heat capacity of the material must be accounted for
Calculating energy change
Q=mcΔt
o Q=heat energy given out or taken in by reaction (J)
o M=mass of surroundings (g)
o C=specific heat capacity of surroundings (J/K/G)
o Δt= change in temperature of surroundings (k)
Always negative when exothermic, positive when endothermic
Flame calorimetry
For combustion reactions
E.g. Burning ethanol
o System is ethanol being burnt
o Surroundings is beaker of water being heated up
o Temp change of water is measured
o However- NOT ALL TEMP CHANGE IS PRESENTED IN WATER- heat energy can escape
o To reduce heat loss, amount of water can be increased or you can use a bomb
calorimeter
Bomb calorimetry
For combustion reactions
Metal container (Bomb) placed in known mass of water
Reaction is started by ignition wires until it has run to completion
Heat energy produced by reaction transferred to bomb
Water surrounded by air surrounded by metal prevents any heat energy being lost
Temp of water is what is used to calculate energy change
Bomb calorimeters are very expensive
Constant pressure calorimetry
For reactions in solutions
Type 1
o Polystyrene cup with copper sulphate solution with thermometer
o Add known quantity of zinc
o System is zinc reacting with copper sulphate ions
o Surroundings is water that the copper sulphate was dissolved in
o Temp change can be used to calculate enthalpy change
o Polystyrene cup can provide insulation
Type 2
Enthalpy change
When experiencing the same change of heat energy, a material with a greater mass will
increase in temperature less than the material with the lesser mass
Water has a specific heat capacity of 4.2J
SHC (J/K/G)- the amount of heat energy it takes to raise 1g of a substance by 1k
When calculating SHC, mass and specific heat capacity of the material must be accounted for
Calculating energy change
Q=mcΔt
o Q=heat energy given out or taken in by reaction (J)
o M=mass of surroundings (g)
o C=specific heat capacity of surroundings (J/K/G)
o Δt= change in temperature of surroundings (k)
Always negative when exothermic, positive when endothermic
Flame calorimetry
For combustion reactions
E.g. Burning ethanol
o System is ethanol being burnt
o Surroundings is beaker of water being heated up
o Temp change of water is measured
o However- NOT ALL TEMP CHANGE IS PRESENTED IN WATER- heat energy can escape
o To reduce heat loss, amount of water can be increased or you can use a bomb
calorimeter
Bomb calorimetry
For combustion reactions
Metal container (Bomb) placed in known mass of water
Reaction is started by ignition wires until it has run to completion
Heat energy produced by reaction transferred to bomb
Water surrounded by air surrounded by metal prevents any heat energy being lost
Temp of water is what is used to calculate energy change
Bomb calorimeters are very expensive
Constant pressure calorimetry
For reactions in solutions
Type 1
o Polystyrene cup with copper sulphate solution with thermometer
o Add known quantity of zinc
o System is zinc reacting with copper sulphate ions
o Surroundings is water that the copper sulphate was dissolved in
o Temp change can be used to calculate enthalpy change
o Polystyrene cup can provide insulation
Type 2
