5-Energy Changes Flashcards
What is an exothermic reaction?
One that transfers energy to the surroundings so the temperature of the surroundings increases
What are examples of exothermic reactions?
*Combustion
*Neutralisation
*Many oxidisation reactions
*Self heating cans
*Hand warmers
What is an endothermic reaction?
One that takes in energy from the surroundings so the temperature of the surroundings decrease
What are examples of endothermic reactions?
*Thermal decompositions
*reactions of citric acid and sodium hydrogencarbonate
*some sports injury packs
What is activation energy
*The minimum amount of energy that particles must have to react
Why are reaction profiles useful?
*they show the relative energies of reactants and products, activation energy and overall change of a reaction
What is the overall energy change of a reaction?
The difference between the sum of energy needed to break bonds and the sum of energy released when bonds in the products are formed
How do cells produce electricity?
Contain chemicals which react to produce electricity
How can a simple cell be made?
Connecting two different metals in contact with an electrolyte
What are batteries?
Two or more cells connected together in series to provide a greater voltage
When does a chemical reaction stop in non-rechargable cells?
*When one of the reactants has been used up
Give an example of a non-rechargable battery.
Alkaline batteries
How can cells and batteries be recharged?
Because the chemical reactions can be reversed when an external electrical current is supplied
How do fuel cells work?
*Supplied by an external force of fuel (e.g hydrogen) and oxygen and air.
*Fuel is oxidised electrochemically within the fuel cell to produce a potential difference
What is the overall reaction in a hydrogen fuel cell?
Involves the oxidisation of hydrogen to produce water
