Energy Changes Flashcards
What is energy change?
Change in heat energy during a reaction
What are the units for energy change?
kJ mol^-1
What is an exothermic reaction?
A reaction where heat is given out
products are lower in energy than reactants
Examples of exothermic reactions
Displacement, neutralisation
What is an endothermic reaction?
A reaction where heat is taken in
reactants are lower in energy than products
Example of endothermic reactions
thermal decomposition
How to calculate energy change using bond energy:
Energy change = sum energy reactants - sum energy products
Why do reactions either give out heat or take it in?
During chemical reactions bonds in reactants must be broken. This takes energy. Bonds must then be formed in the products. This gives out energy.
A reaction is exothermic if … (in terms of bonds broken and formed)
If breaking the bonds in the reaction takes less energy than is given out by the formation of products
A reaction is endothermic if … (in terms of bonds broken and formed)
If breaking the bonds in the reaction takes more energy than is given out by the formation of products
If breaking the bonds in the reaction takes less energy than is given out by the formation of products the reaction will be:
exothermic
If breaking the bonds in the reaction takes more energy than is given out by the formation of products the reaction will be:
endothermic
