energy changes Flashcards
What is conserved when chemical reactions occur?
Energy.
What is the same at the beginning and the end of a chemical reaction in the universe?
The amount of energy.
Exothermic reactions transfer…
Energy to the surroundings.
In exothermic reactions, product molecules must have…
Less energy than the reactants.
What are 3 scientific examples of exothermic reactions?
~Combustion
~Neutralisation
~Many oxidation reactions
What is an everyday example of an exothermic reaction?
Hand warmers.
Endothermic reactions take in…
Energy from the surroundings.
In endothermic reactions, product molecules must have…
More energy than the reactants.
What are 2 scientific examples of endothermic reactions?
~Thermal decomposition
~The reaction of citric acid and sodium hydrogen carbonate
What is an everyday example of an endothermic reaction?
Sports injury packs.
Chemical reactions only occur when…
Reacting particles collide with eachother with sufficient energy.
What is activation energy?
The minimum amount of energy that particles must have to react.
During a chemical reaction, energy must be supplied to…
Break bonds in the reactants.
During a chemical reaction, energy is released when…
Bonds in the products are formed.
What is the bond energies calculation?
Sum of energy taken in to break bonds - sum of energy released to form bonds = overall energy change
If the energy taken in to break bonds is greater than the energy released when bonds are formed, what type of reaction is it and why?
Endothermic as the overall energy has been taken in.
If the energy taken in to break bonds is smaller than the energy released when bonds are formed, what type of reaction is it and why?
Exothermic as the overall energy has been released.
What so chemicals in cells react to produce?
Electricity.
What is a factor that affects the voltage produced by a cell?
The type of electrode and electrolyte.
How is a simple cell made?
By connecting 2 different metals in contact with an electrolyte.
What is a battery?
2 or more cells connected together in series to provide a greater voltage.
When do chemical reactions stop in non-rechargeable cells and batteries?
When one of the reactants is used up.
What type of battery is non-rechargeable?
Alkaline batteries.
Why can rechargeable cells and batteries be recharged?
As the chemical reactions are reversed when an external electrical current is supplied.
What are fuel cells supplied by?
An external source of fuel ( eg. hydrogen ) and oxygen.
What does the fuel inside a fuel cell produce when it is oxidised electrochemically?
A potential difference.
An overall reaction of a hydrogen fuel cell involves…
The oxidation of hydrogen to produce water.
What are a potential alternative to rechargeable cells and batteries?
Hydrogen fuel cells.
Hydrogen fuel cells can be used constantly as long as…
Fuel is continually being put in.
Why are hydrogen fuel cells harder to transport than rechargeable cells and batteries?
As hydrogen is a gas and therefore needs to be stored at a high pressure.
Why don’t rechargeable cells and batteries need to be constantly supplied?
As they can be recharged by reversing the reaction.
Why are rechargeable cells and batteries hard to dispose of?
They are non-biodegradable.
