Energy Changes for Separate Science

Give 3 examples of exothermic reactions

Combustion Many Oxidation reactions Neutralisations

Give a use of an endothermic reaction

Sports injury packs

Give two examples of endothermic reactions

Thermal decomposition The reaction of citric acid and sodium hydrogencarbonate

Give two uses of exothermic reactions

Self-Heating Cans Hand Warmers

How are fuel cells supplied?

an external source of fuel (e.g. hydrogen) and oxygen/air

How can rechargeable cells and batteries be recharged?

The chemical reactions are reversed when an external electrical current is supplied

How do you make a simple cell?

Connecting two different metals in contact with an electrolyte

If the energy released from forming new bonds is greater than the energy needed to break existing bonds then the reaction is

Exothermic

If the energy released from forming new bonds is less than the energy needed to break existing bonds then the reaction is

Endothermic

What are the pros and cons hydrogen fuel cell?

Pros - easy to maintain, small size, water is only chemical product Cons - very expensive, need a constant supply of hydrogen fuel, flammable

What are the pros and cons of alkaline cells?

Pro - cheaper to manufacture Cons - may end up in landfill sites/expensive to recycle

What are the pros and cons rechargeable batteries?

Pros - can be recharged many times before recycled Cons - costs more to manufacture

What batteries are non-rechargeable?

Alkaline

What do batteries consist of?

Two or more cells connected in a series to provide a greater voltage

What do cells contain which react to produce electricity?

Chemicals

What do we call the minimum amount of energy that particles must have to react?

Activation energy

What factors will affect the voltage the cell produces?

Type of electrode Type of electrolyte

What happens for a non-rechargeable cell of battery to stop working?

The chemical reactions stops as the reactants are used up

What happens in a fuel cell?

Fuel oxidised electrochemically

What is produced by a fuel cell?

Potential difference

What is the equation for the two half equations added together?

2H2 + 4OH- + O2 + 2H2O + 4e- → 4H2O + 4e- + 4OH-

What is the equation of a fuel cell?

2H2(g) + O2(g) → 2H2O(l)

What is the half equation for a fuel cell at the anode?

O2 + 2H2O + 4e- → 4OH-

What is the half equation for a fuel cell at the cathode?

2H2 + 4OH- → 4H2O + 4e-

What product is produced by a hydrogen fuel cell?

Water

What reaction is involved i

Oxidation of hydrogen

What type of reaction takes in energy from the surroundings, so the temperature of the surroundings decreases

Endothermic

What type of reaction transfers energy to the surroundings, so the temperature of the surroundings increases?

Exothermic

When bonds are broken in the reactants is energy supplied or released?

Supplied

When bonds in the products are formed is energy supplied or released

Released

When do chemical reactions occur?

When particles: Collide with each other With Sufficient energy