C7: Energy Changes Flashcards
Give examples of exothermic reactions
Combustion, many oxidation and neutralisation
What are some everyday uses of exothermic reactions?
Self-heating cans and hand warmers
Give examples of endothermic reactions
Thermal decomposition and the reaction between citric acid and sodium hydrogencarbonate
What is an everyday use of endothermic reactions?
Some sports injury packs
What is activation energy?
The minimum amount of energy required to start a reaction
How does the energy released from forming new bonds differ to the energy needed to break existing bonds in an exothermic reaction?
Energy released is greater
What do cells contain?
Chemicals which react to produce electricity
What factors affect the voltage that a cell produces?
The electrode and electrolyte used
How can a simple cell be made?
By connecting 2 different metals in contact with an electrolyte
What makes cells and batteries non-rechargeable?
The fact that the chemical reactions stop when one of the reactants has been used up
What makes cells and batteries rechargeable?
The fact that the chemical reactions are reversed when an external electrical current is supplied
How do fuel cells work?
They are supplied by an external source of fuel (e.g. hydrogen) and oxygen or air. The fuel is oxidised electrochemically within the fuel cell to produce an electric current
What is the overall reaction in a hydrogen fuel cell?
The oxidation of hydrogen to produce water
What type of battery is found in wireless headphones?
Rechargeable
What is the negative electrode in a hydrogen-oxygen fuel cell?
Anode
