Flashcards in Unit 5-Energy changes Deck (25):
Why may products store more energy than the original reactants?
They must have taken in energy from the surroundings.
Why might products of a reactions store less energy than the original reactants?
Energy must have been transferred to the surroundings.
What is an exothermic reaction?
A reaction where it transfers energy to the surroundings,usually by heating.
What is an endothermic reaction?
A reaction that takes in energy from the surroundings.
What is combustion ?
In an exothermic reaction what happens to the temperature?
In an endothermic reaction what happens to the temperature?
Are neutralisation reactions exothermic or endothermic?
Give two examples of exothermic reactions in every day life.
-Self heating cans of hot chocolate.
Give an example of an endothermic reaction.
Sports injury packs because the chemical reaction allows it to become instantly cooler without a fridge.
What are reaction profiles?
Diagrams that show the relative energies of the reactants and products in a reaction.
What is the activation energy in a reaction profile?
The minimum amount of energy reactants need to collide with each other.
Is bond breaking an exothermic or endothermic reaction?
Is bond formation an endothermic or exothermic reaction?
Why may you not be able to compare overall energy changes of reactions?
You need to know the numerical differences.
What is an electrochemical cell?
A basic system made up of two different electrodes in contact with an electrolyte.
What can cause charge difference in cells?
Different metals will react differently with the same electrolyte.
The bigger the difference in reactivity of the electrodes the ...
Bigger the voltage of the cell.
How is a battery formed?
By connecting two or more cells together in a series.
Why do rechargeable batteries work?
Because in a rechargeable cell the reaction can be reversed connecting it to an external electric current.
What is a fuel cell?
An electrical cell that’s supplied with a fuel and oxygen and uses energy from the reaction between them to produce electrical energy efficiently.
What happens when fuel enters a cell?
It becomes oxidised and sets up a potential difference within the cell.
What’s the advantage to fuel cells?
The don’t produce as many pollutants for cars.
What’s a disadvantage to fuel cells?
Although when being used they are better for the environment,when they are disposed of they are very polluting.