Unit 13 - Energetics
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A reaction is which heat energy is given out
Exothermic This is because making bonds is exothermic
A reaction on which heat energy is taken in
Endothermic This is because the breaking of bonds is endothermic
What is enthalpy change
The enthalpy change for a reaction, △H, is the heat change per mole when reactants change into products
Enthalpy change (△H) for exoteric reactions
Negative, since they lost heat from giving it out
Enthalpy change (△H) for an endothermic reaction
Positive, since it took in heat
Describe a simple calorimeters experiment where heat energy changes can be measured from temperature changes
Measure the temperature at the beginning of the experiment, measure the temperature at the end. How ever much heat has gone up or down is the calorimetry of the reaction.
calculate molar enthalpy change from heat energy change
ΔH = temperate change X specific heat capacity X mass/volume
What specific heat capacity
The energy (number of joules) needed to make 1cm3 (or 1g) of substance rise by 1 degree Celsius
Use average bond energies to work out energy change in a reaction
(You’ll get given bind energies for each molecule needed) To work out the enthalpy change (△H)you do: the sum of bond energies in the reactants - the sum of bond energies in the product
Representing exothermic reactions on an energy level diagram
The reactants are above the products
Representing endothermic reactions on an energy level diagram
The reactants are below the products