What is an exothermic reaction?
A reaction that transfers energy to the surroundings so the temperature of the surroundings increases
Give examples of exothermic reactions
- combustion(fuels burnt in the presence of oxygen)
- oxidation reactions
- neutralisation
Give everyday uses of exothermic reactions
- self-heating cans
- hand warmers
What is an endothermic reaction?
A reaction that takes in energy from the surroundings so the temperature of the surroundings decreases
Give examples of endothermic reactions
- thermal decomposition
- reaction of citric acid and sodium hydrogen carbonate
What does a reaction profile show?
The relative energies of reactants and products, the activation energy and the overall energy change of a reaction
Which is higher in an exothermic reaction profile: reactants or products?
Reactants
Which is higher in an endothermic reaction profile: reactants or products?
Products
When there is a positive temperature change, what type of reaction is it?
exothermic
When there is a negative temperature change, what type of reaction is it?
Endothermic
When there is an overall positive energy change, what type of reaction is it?
endothermic
When there is an overall negative energy change, what type of reaction is it?
Exothermic
What is activation energy?
The minimum energy needed by the particles (of the reactants) in order for them to collide for a reaction to occur
When the chemical bonds in reactants are broken down what happens?
Energy is taken from the surroundings to break the bonds= endothermic
What does ‘bond energy’ mean?
The amount of energy needed to break the bond between one mole of a particular covalent bond
When the chemical bonds in the products are formed what happens?
energy is released when the new chemical bonds form = exothermic
overall energy change equation?
energy needed to break bonds(of the reactants) - energy released when forming new bonds (of the products)
Explain the relationship between energy needed to break bonds and energy released to form new bonds in an exothermic reaction
The energy released when forming new bonds is greater so there is a negative total energy change as energy is lost to the surroundings
Explain the relationship between energy needed to break bonds and energy released to form new bonds in an endothermic reaction
the energy required to break bonds is greater than the energy released when forming bonds so there is positive total energy change which tells us how much more energy has been gained by the surroundings
What is the voltage produced by a cell dependent on?
- type of electrode
- type of electrolyte
How can a simple cell be made?
by connecting two different metals in contact with an electrolyte
