Energy Changes Flashcards
(33 cards)
What happens to energy during a chemical reaction?
Energy is conserved — the total energy at the start equals the total at the end.
What is an exothermic reaction?
A reaction that transfers energy to the surroundings, increasing temperature.
What are some examples of exothermic reactions?
Combustion, oxidation, neutralisation reactions.
Name everyday uses of exothermic reactions.
Self-heating cans and hand warmers.
What is an endothermic reaction?
A reaction that takes in energy from the surroundings, decreasing temperature.
What are examples of endothermic reactions?
Thermal decomposition and citric acid + sodium hydrogencarbonate.
Name a practical use of endothermic reactions.
Cold packs for sports injuries.
What do reaction profiles show?
The relative energies of reactants and products, activation energy, and energy change.
What is activation energy?
The minimum energy required for particles to react during a collision.
How can you tell from a reaction profile if a reaction is exothermic?
Products have less energy than reactants; energy is released.
How can you tell from a reaction profile if a reaction is endothermic?
Products have more energy than reactants; energy is absorbed.
What must happen for a chemical reaction to occur?
Particles must collide with sufficient energy.
What is required to break bonds in a chemical reaction?
Energy must be supplied to break bonds.
What happens when bonds are formed in a chemical reaction?
Energy is released.
How do you calculate the overall energy change in a reaction?
Energy to break bonds – energy released forming bonds.
When is a reaction overall endothermic (bond energies)?
When more energy is taken in to break bonds than released when forming bonds.
When is a reaction overall exothermic (bond energies)?
When more energy is released forming bonds than taken in to break bonds.
What do chemical cells contain?
Chemicals that react to produce electricity.
What affects the voltage of a chemical cell?
The type of electrode and electrolyte.
How is a simple cell made?
By connecting two different metals in contact with an electrolyte.
What is a battery?
Two or more cells connected in series to provide a greater voltage.
What happens in a non-rechargeable cell or battery?
The reaction stops when one of the reactants is used up.
Are alkaline batteries rechargeable?
No, they are non-rechargeable.
What is a rechargeable battery?
A battery that can be recharged by reversing the chemical reactions with an external current.
