AQA GCSE Chemistry Unit 5 Energy Changes

Flashcards for AQA GCSE Chemistry Unit 5: Energy Changes, covering exothermic and endothermic reactions, reaction profiles, bond energies, chemical cells, and fuel cells.

What type of reaction involves the transfer of energy from reacting chemicals to the surroundings?

Exothermic reaction

What happens to the temperature during an exothermic reaction in a practical investigation?

The temperature increases.

Give three examples of exothermic reactions.

Combustion, respiration, and neutralization reactions

Give some everyday examples of exothermic reactions.

Hand-warmers and self-heating cans

What type of reaction involves the transfer of energy from the surroundings to the reacting chemicals?

Endothermic reaction

What happens to the temperature during an endothermic reaction in a practical investigation?

The temperature decreases.

Give an example of an endothermic reaction.

Thermal decomposition of calcium carbonate

Give some everyday examples of endothermic reactions.

Eating sherbet and instant ice packs

In an exothermic reaction profile, are the reactants at a higher or lower energy level than the products?

Higher energy level

What happens to the energy in an exothermic reaction?

Energy is released to the surroundings.

In an endothermic reaction profile, are the reactants at a higher or lower energy level than the products?

Lower energy level

What happens to the energy in an endothermic reaction?

Energy is absorbed from the surroundings.

Define activation energy.

The minimum amount of energy required for a chemical reaction to take place.

How do catalysts affect the rate of a reaction?

Catalysts increase the rate of a reaction.

How do catalysts lower the activation energy?

By Providing an alternate pathway for a chemical reaction to take place.

Is energy needed to break chemical bonds in an endothermic reaction or an exothermic reaction?

Endothermic reaction

Is the energy change (ΔH) positive or negative in an endothermic reaction?

Positive

Is energy needed to form chemical bonds in an endothermic reaction or an exothermic reaction?

Exothermic reaction

Is the energy change (ΔH) positive or negative in an exothermic reaction?

Negative

In calculations using bond energies, what is the formula to find the change in energy?

ΔH = sum (bonds broken) - sum (bonds made)

What type of energy is converted to electrical energy in a chemical cell?

Chemical energy

What is a battery?

More than one cell connected in series

What happens to non-rechargeable cells when the chemicals inside are used up?

The cell is no longer useful.

How do rechargeable cells work?

An electrical current is passed backwards through the cell, reversing the chemical reactions.

What affects the voltage of a chemical cell?

The combination of metals used inside it.

How is the voltage affected by the difference in the reactivity of the two metals?

The bigger the difference in the reactivity of the two metals, the bigger the voltage produced.

What two components are needed continuously in a fuel cell to produce voltage?

Fuel and oxygen

What is oxidized electrochemically inside the fuel cell?

Hydrogen

What is the only product produced by hydrogen-oxygen fuel cells?

Water

In a fuel cell, is oxygen being reduced or oxidized?

Reduced

In a fuel cell, is hydrogen being reduced or oxidized?

Oxidized

What is the name of a reaction where oxidation and reduction happen simultaneously?

Redox reaction