C5 - Energy Changes Flashcards
(22 cards)
What happens in an exothermic reaction?
Energy is given out to the surroundings
What happens to the temperature of surroundings in exothermic reactions?
Increases
Types of exothermic reactions?
- Combustion
- Oxidation
- Neutralisation
Two specific exothermic reactions?
- Hand warmers
- Self heating cans of food and drinks
What happens in endothermic reactions?
Energy is taken in from the surroundings
What happens to the temperature of the surroundings in an endothermic reaction?
Decreases
Types of endothermic reactions?
- Electrolysis
- Thermal decomposition
- Photosynthesis
Specific endothermic reaction?
Cold packs for sports injuries
What is activation energy?
The minimum amount of energy required for a successful collision
What is on the x axis on a reaction profile?
Energy
What is on the y axis on a reaction profile?
Progress of reaction
What is bond energy?
The amount of energy required to break the bond or the amount of energy given out when the bond is formed
How do you calculate energy change?
Energy taken in - Energy given out
What is a chemical cell?
A source of electrical energy
Why are alkali batteries not rechargeable?
The reactions are irreversible so when one of the reactants are used up, the battery cannot be used
How can rechargeable batteries be charged?
The reactions are reversed by connecting the cells to an external electrical supply
How does a hydrogen cell work?
Hydrogen enters at the anode where it is oxidised and oxygen enters at the cathode where it is reduced
Half equation that occurs at the cathode?
2H2 –> 4H+ + 4e-
Half equation that occurs at the anode?
4H+ + O2 + 4e- –> 2H2O
Overall reaction in a fuel cell?
2H2 + O2 –> 2H20
Advantages of hydrogen fuel cell?
- Produce no pollution
- Produce more energy per kg than either petrol or diesel
- No batteries to dispose of which is better for environment
- Continuous process so will keep producing energy as long as fuel is supplied
Disadvantages of hydrogen fuel cell?
- Materials used to produce fuel cells are expensive
- High pressure tanks needed for oxygen and hydrogen which is dangerous and difficult
- Affected at low temperature, becoming less efficient
- Hydrogen is expensive to produce and store
