C3.3.1 Energy from reactions Flashcards
What is calirometry?
Measuring the amount of energy transferred during a reaction.
Give a basic example of a calirometry experiment.
Heating water in a glass or metal container and measuring the temperature change.
What equation do you use to measure the amount of energy released by a fuel?
Q = mc ΔT
Q = energy transferred m = mass c = specific heat capacity ΔT = change in temperature
What happens to the bonds in a chemical reaction?
The bonds in the reactants are broken.
New bonds are created in the products.
Breaking bonds _______ energy.
Breaking bonds REQUIRES energy.
Making bonds _______ energy.
Making bonds RELEASES energy.
Describe an exothermic reaction.
Exothermic reactions give out heat energy to the surroundings.
Negative energy change - products have less energy than reactants.
Give 2 examples of exothermic reactions.
Combustion
Neutralisation reactions (acids + alkali)
Describe an endothermic reaction.
Endothermic reactions absorb heat energy from the surroundings.
Positive energy change - products have more energy than reactants.
Give 2 examples of endothermic reactions.
Electrolysis
Reaction between ethanoic acid and sodium carbonate
What is activation energy?
Energy that is supplied to the reactants to start a reaction.
What is a catalyst?
A substance that speeds up the rate of a chemical reaction without being used up in the reaction.
How does a catalyst work?
They provide a different pathway for the reaction to follow with a lower activation energy than the one followed by the uncatalysed reaction.
As a result, a greater proportion of reacting particles have enough energy to react.
How can hydrogen be used as a fuel in cars?
Burning hydrogen directly in the engine
Hydrogen fuel cells where the hydrogen reacts with oxygen without burning.
Give 2 benefits of using hydrogen to power cars.
Hydrogen does not generate carbon dioxide when burnt
Hydrogen fuel cells are very efficient
Give 3 disadvantages of using hydrogen.
Hydrogen is not highly available from petrol stations
Hydrogen is difficult to store safely
The production of hydrogen uses fossil fuels
How do you calculate bond energies?
Add together all the bond energies for all the bonds in the reactants.
Add together the bond energies for all the bonds in the products.
Calculate the energy change.
