Chemistry - Enthalpy change experiments

Fuel burnt for longer period of time

Enthalpy change same (temp change larger, energy released larger but moles burnt also is larger)

Calc error gave lower mass of fuel than used

Enthalpy change more exothermic (energy released same, moles burnt smaller)

Larger volume of water used

Enthalpy change is the same (temp change less, but mass is larger so energy released same)

Incomplete combustion occurs

Enthalpy change less exothermic (temp change smaller, energy released smaller)

Some water spills out before alcohol is burned

Enthalpy change more exothermic (temp change larger, energy released larger)

Some alcohol evaporated before spirit burned was reweighed

Enthalpy change less exothermic (mass of spirit burner smaller, moles burned would be larger)

Molar mass of ethanol used instead of propanol

Enthalpy change less exothermic (Mr of ethanol less, moles burned larger)

Water was boiled for 5 minutes before the final temperature was taken

Enthalpy change same (temp remains constant as state change to gas, latent heat of vapourisation)

Enthalpy change of a reaction

Enthalpy change that accompanies a reaction in the molar quantities expressed in a chemical equation under standard conditions

Enthalpy change of neutralisation

The enthalpy change the accompanies the formation of one mole of water from neutralisation, under standard conditions.

The enthalpy change of formation

The enthalpy change when one mole of a compound is formed from its elements under standard conditions.

The enthalpy change of combustion

The enthalpy change for complete combustion of one mole of a substance under standard conditions.

Calculate enthalpy change of a reaction

1) Find Q=mcΔT 2)Convert Q to kJ 3) Find moles of substance used 4) Find ΔH= Q/moles 5) Add sign

Calculate enthalpy change of neutralisation and solution

1) Find Q=mcΔT (use total volume of solution) 2) Find moles of water produced (use reactant not in excess) 3) Find ΔH=Q(kJ)/moles water 4) Add sign

Calculate enthalpy change of combustion

1) Find Q=mcΔT using mass of water 2) Convert Q to kJ 3) Find moles of combusted reactant 4) Find ΔH=Q/moles 5) Add sign