C5-Energy Changes
Cards (19)
- An exothermic reaction is one that transfers energy to the surroundings
- Exothermic reaction cause the temperature of the surroundings to increase
- Examples of exothermic reactions :
- Combustion
- Oxidation
- Neutralisation
- Everyday uses of exothermic reactions :
- Hand warmers
- Self-heating cans
- An endothermic reaction is one that takes in energy from the surroundings
- Endothermic reactions cause the temperatures of the surroundings to decrease
- Examples of endothermic reactions :
- Thermal decomposition
- Everyday uses of endothermic reactions :
- Sports injury packs
- Practical : Temperature Change
- Measure 25 cm3 of hydrochloric acid and sodium hydroxide in separate beakers
- Place the beakers in a water bath set to 25∘C until they are the same temperature
- Add the HCL and the NaOH to a polysytrene that is surrounded by cotton wool to reduce heat loss
- Take temperature recordings every 30 seconds and record the highest temperature
- Repeat the steps with different concentrations of hydrochloric acid
- Reaction profile for exothermic reactions :
- Reaction profile for endothermic reactions :
- In exothermic reactions, more energy is released by the bonds formed in the products than is used in breaking the bonds of the reactants
- In endothermic reactions, the energy released in making bonds is less than what is used to break bonds and so the reaction absorbs energy
- Bond energy calculations :Energy Change = Sum of Bonds Broken - Sum of Bonds Made
- If the energy change is :
- negative the reaction is exothermic
- positive the reaction is endothermic
- Factors affecting cell voltage:
- Electrolyte
- Difference in reactivity of electrodes
- Non rechargeable batteries:
- When reactant gets used up
- Irreversible reaction
- Fuel cells:
- Uses fuel, oxygen and energy to produce electrical energy efficiently
- Hydrogen-oxygen fuel cells:
- Less pollution, cheaper, recharged less often
- Takes up more storage, harder to store safely, made from fossil fuels