5. Energy changes (exothermic & endothermic reactions, reaction profiles, energy change of reactions, required practical 4) Flashcards
What happens to energy in chemical reactions?
It is conserved
If a reaction transfers energy to the surroundings, what must that mean?
The product molecules must have less energy than the reactants, by the amount transferred
What is an exothermic reaction?
A reaction that transfers energy to the surroundings , so the temperature of the surroundings increases
What are examples of exothermic reactions?
- combustion
- many oxidation reactions - neutralisation
What are everyday examples of exothermic reactions?
- self-heating cans (e.g. for coffee)
- hand warmers
What is an endothermic reaction?
A reaction that takes in energy from the surroundings, so the temperature of the surroundings decreases
What are examples of endothermic reactions?
- thermal decompositions
- reaction of citric acid and sodium hydrogencarbonate
What is an everyday example of an endothermic reaction?
some sports injury packs
When only can chemical reactions occur?
When reacting particles collide with each other and with sufficient energy
What is activation energy?
The minimum amount of energy that particles must have to react
What can reaction profiles be used to show?
- the relative energies of reactants and products
- the activation energy
- the overall energy change of a reaction
How can you tell, on a reaction profile, whether the reaction is exothermic or endothermic?
By looking at whether the reactants or products have more energy
Do the reactants or products have more energy in an exothermic reaction?
products have less
energy than reactants
Do the reactants or products have more energy in an endothermic reaction?
so products have more energy than reactants
In a reaction, what must be supplied to break the bonds in the reactants?
Energy
