C5 Flashcards
What is an exothermic reaction?
A reaction that gives OUT heat energy.
What is an endothermic reaction?
A reaction that TAKES in heat energy.
Give three examples of exothermic reactions.
Combustion
Respiration
Neutralisation
What happens to the temperature of the surroundings (as shown on a thermometer) in an exothermic reaction.
Temperature goes up
What uses are there for exothermic reactions?
Fuels being combusted for heat
Self-heating cans
Hand-warmers
State a use for endothermic reactions.
Sport injury packs
What must happen for a reaction to happen?
Reactant particles must collide with enough energy - (activation energy)
What is meant by the term activation energy.
The minimum energy needed for a reaction to start.
Is the breaking of bonds exothermic or endothermic?
Endothermic
Is the making of bonds exothermic or endothermic?
Exothermic
Why is a reaction exothermic?
Less heat energy is needed to break bonds than the heat energy given out.
Why is a reaction endothermic?
Less energy is released in making bonds in the products than is required in breaking bonds in the reactants.
How do you calculate the energy change in a reaction?
Energy created from bonds - energy needed to break bonds
Negative answer = exothermic
Positive answer = endothermic
How do cells produce electricity?
The chemicals in them react.
What is a simple cell?
2 different metals and an electrolyte.
When will 2 metals in a cell produce a bigger voltage?
If they have a wider gap in their reactivities.
What is a battery?
2 or more cells connected in a series
Why do non rechargeable batteries like alkaline batteries run out?
When one of the reactants is used up the chemical reaction stops
Why can rechargeable batteries be recharged?
The chemical reaction is reversed when a current is applied to make the original reactants again.
What do fuel cells use to produce electricity?
A fuel (hydrogen) and oxygen.
What is the overall equation for the reaction in a hydrogen fuel cell?
2H(2) + O(2) ——-> water
What is an advantage of a fuel cell over a rechargeable cell?
Fuels can be supplied constantly to generate electricity
What is a disadvantage of a fuel cell over a rechargeable cell?
Hydrogen is flammable
Give 2 examples of endothermic reactions.
Photosynthesis
Thermal decomposition
