C5 Energy Changes

Created by

Amelia Taunton

Cards (32)

What happens to energy in a chemical reaction?
It is transferred from the chemicals to or from the surroundings
What does the transfer of energy in a chemical reaction mean?
Many reactions are accompanied by a temperature change
What are exothermic reactions?
Reactions that are accompanied by a temperature rise.
They transfer heat energy from the chemicals to the surroundings, i.e. they give out heat energy
What are endothermic reactions?
Reactions that are accompanied by a fall in temperature.
Heat energy is transferred from the surroundings to the chemicals, i.e. they take in heat energy.
What are endothermic reactions used in?
Sports injury packs
What does a reversible reaction do with energy transfers?
If it is exothermic in one direction, it is endothermic in the opposite direction.
The same amount of energy is transferred in each case.
Why are atoms rearranged in chemical reactions?
Old bonds are broken and new bonds are formed.
What is needed for bonds to be broken?
Reacting particles must collide with sufficient energy.
What is activation energy?
The minimum amount of energy that the particles must have for a reaction to take place.
How can energy changes in a reaction between shown?
Using energy level diagrams or reaction profiles.
During an exothermic reaction?
Energy is given out to the surroundings.
The products have less energy than the reactants.
During an endothermic reaction?
Energy is being taken in from the surroundings.
The products have more energy than the reactants.
What do catalysts do?
Reduce the activation energy needed for a reaction, this increases the rate of reaction.
What type of process is breaking a chemical bond?
It requires energy, so it is endothermic
What type of process is forming a new chemical bond?
Energy is given out, so it is exothermic
What energy change shows the reaction is endothermic?
If more energy is required to break bonds than is released when bonds are formed.
What energy change shows the reaction is exothermic?
If more energy is released when bonds are formed than is needed to break bonds
How can the amount of energy produced in a reaction be measured?
By mixing the reactants in an insulated container.
This enables the temperature change to be measured before heat is lost to the surroundings.
This method is suitable for neutralisation reactions and reactions involving solids.
What do chemicals in cells react together to release?
Electricity
How can a simple cell be made?
By placing two different metals into a beaker containing an electrolyte
How are batteries made?
When two or more cells are connected together.
What is the voltage produced by a cell dependant on?
Type of electrode and electrolyte used.
What can cells joined in series produced?
A higher voltage
When do non-rechargable batteries stop producing electricity?
When one of the reactants has been used up.
What are fuel cells?
An efficient way of producing electrical energy
What do most fuel cells use?
Hydrogen, but other fuels can be used.
What happens in a hydrogen fuel cell?
Hydrogen and oxygen are supplied to the fuel cell.
The fuel is oxidised to produce a potential difference (voltage).
Overall, the hydrogen is oxidised to form water
Where is hydrogen added in fuel cells?
At the anode.
The hydrogen molecules lose electrons to form hydrogen ions.
2H2 > 4H+ + 4e-
Where is oxygen added in fuel cells?
At the cathode.
The hydrogen ions formed at the anode travel through the electrolyte to the cathode, where they react with oxygen molecules to form water.
O2 + 4H+ + 4e- > 2H2O
What is the overall equation for the reaction in the hydrogen fuel cell?
2H2 + O2 > 2H2O
What do traditional methods of producing electricity involve?
Many stages and are less efficient and more polluting than fuel cells.
What are advantages of fuel cells?
Hydrogen fuel cells produce water, which is non-polluting.
They are lightweight and small.
They have no moving parts so are very unlikely to break down.