Exothermic and Endothermic Reactions Flashcards
Energy Changes (26 cards)
What do chemicals store?
A certain amount of energy
Different chemicals store different amounts of energy.
What happens if the products of a reaction store more energy than the original reactants?
They must have taken in the difference in energy from the surroundings during the reaction.
What occurs if the products store less energy than the reactants?
The wrong energy was transferred to the surroundings during the reaction.
What principle explains the conservation of energy in reactions?
Energy is conserved in reactions - it can’t be created or destroyed, only moved around.
What is an Exothermic Reaction?
A reaction that transfers energy to the surroundings, usually by heating.
What indicates that an exothermic reaction is occurring?
A rise in temperature.
What is the best example of an exothermic reaction?
Burning fuels (combustion).
What is another example of an exothermic reaction?
Neutralisation reactions (acid + alkali).
What happens when sodium is added to water?
It releases energy, indicating it is an exothermic reaction.
What are some everyday uses of exothermic reactions?
- Band warmers using oxidation of iron in air
- Self-heating cans for hot chocolate and coffee.
What is an Endothermic Reaction?
A reaction that takes in energy from the surroundings.
What indicates that an endothermic reaction is occurring?
A fall in temperature.
Are endothermic reactions more or less common than exothermic reactions?
Less common.
What is an example of an endothermic reaction?
The reaction between citric acid and sodium hydrogen carbonate.
What is thermal decomposition?
A process where heating calcium carbonate causes it to decompose into calcium oxide and carbon dioxide.
What is the equation for the thermal decomposition of calcium carbonate?
CaCO3 (+ HEAT) → CO2 + CaO (Quicklime)
How are endothermic reactions used in sports injury packs?
The chemical reaction allows the pack to become instantly cooler.
What is a reaction profile?
Diagrams that show the relative energies of the reactants and products in a reaction and how the energy changes over the course of the reaction.
What type of reaction is shown when the products are at a lower energy than the reactants?
Exothermic reaction.
What does the difference in height in a reaction profile represent?
The overall energy change in the reaction (the energy given out or taken in) per mole.
What does the initial rise in energy in a reaction profile indicate?
The energy needed to start the reaction, known as the activation energy (E_a).
What is activation energy?
The minimum amount of energy the reactants need to collide with each other and react.
True or False: The greater the activation energy, the less energy is needed to start the reaction.
False.
How can activation energy be supplied to a reaction?
By heating the reaction mixture.
