9. Energy Changes Flashcards
What happens to energy when chemical reactions occur?
Energy is transferred to or from the surroundings. Exothermic reactions release energy, while endothermic reactions absorb energy.
What is an exothermic reaction and give examples?
An exothermic reaction transfers energy to the surroundings. Examples include combustion, oxidation reactions, and neutralisation.
Everyday uses include self-heating cans and hand warmers.
What is an endothermic reaction and give examples?
An endothermic reaction takes in energy from the surroundings.
Examples include thermal decompositions and some sports injury packs.
What are reversible reactions and how are they represented?
Reversible reactions are those where the products can react to form the original reactants. They are represented as:
𝐴 + 𝐵 ⇌ 𝐶 + 𝐷
How can the relative amounts of energy released by burning substances be measured?
By simple calorimetry, such as heating water in a glass or metal container.
In what units is energy normally measured?
Energy is normally measured in joules (J) or kilojoules (kJ)
How can the amount of energy produced by a chemical reaction in solution be calculated?
From the measured temperature change of the solution when reagents are mixed in an insulated container using the equation: 𝑄 = 𝑚𝑐Δ𝑇
What do simple energy level diagrams show?
They show the relative energies of reactants and products, the activation energy, and the overall energy change of a reaction.
What happens to energy during a chemical reaction?
Energy is supplied to break bonds and released when new bonds are formed.
What happens to energy in an exothermic reaction?
The energy released from forming new bonds is greater than the energy needed to break existing bonds.
What happens to energy in an endothermic reaction?
The energy needed to break existing bonds is greater than the energy released from forming new bonds.
How do catalysts affect chemical reactions?
Catalysts provide a different pathway for a chemical reaction with a lower activation energy.
What is a chemical cell?
A chemical cell produces a potential difference until the reactants are used up
How do fuel cells produce electricity and what is an example?
Fuel cells produce electricity through the reaction of a fuel with oxygen.
An example is the hydrogen-oxygen fuel cell, which uses hydrogen as fuel and produces water as the only waste product.
What are the advantages and disadvantages of hydrogen fuel?
Advantages:
- less pollution as the only waste
product is water.
Disadvantages:
- challenges in storage and use
- considerations of products of
combustion.
