Topic 5 - Energy Changes Flashcards
What happens to energy in chemical reactions?
It is conserved
Is energy lost during chemical reactions?
No it is transferred but never lost
What is an exothermic reactions?
Transfers energy to the surroundings so the temperature of the surroundings increases
Give examples of exothermic reactions
Combustion, oxidation, neutralisation
Give examples of everyday uses exothermic reactions?
Self heating cans and handwarmers
What is an endothermic reaction?
One that takes energy in from the surroundings to the temperature of the surroundings decreases
Give examples of endothermic reactions
Thermal decompositions
The reaction of citric acid and sodium hydrogencarbonate
Give an example of everyday use of endothermic reactions
Sports injury packs
When can chemical reactions occur?
Only 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 do reaction profiles show?
The relative energies of reactants and products
The activation energy
The overall energy change of a reaction
What needs to happen during a chemical reaction?
Energy must be supplied to break bonds in the reactants
Energy is released when bonds in the products are formed
Describe the bond energies of an endothermic reaction?
The energy needed to break existing bonds is greater than the energy released from forming new bonds
What do cells contain?
Chemicals which react to produce electricity
What is the voltage produced by a self dependent on?
Type of electrode and electrolyte
How can you make a simple cell?
Connecting to different metals in contact with an electrolytes
What do batteries consist of?
Two or more cells connected together in a series to provide greater voltage
What happens to chemical reactions in nonrechargeable cells and batteries?
They stop when one of the reactants has been used up
Give an example of a non-rechargeable battery
Alkaline batteries
Why can rechargeable cells and batteries be recharged?
Because the chemical reactions are reversed when an external electrical current is supplied
What are fuel cells?
They are supplied by an external source of fuel and oxygen or air
How do fuel cells work?
The fuel is oxidised electrochemically within the fuel cell to produce a potential difference
What does the overall reaction in a hydrogen fuel cell involve?
The oxidation of hydrogen to produce water
Why are fuel cells better for the environment?
Don’t produce as many pollutants
