Topic 5: Energy Changes (AQA Chemistry – Combined Science)
No description yet. This curated deck is ready for daily study.
Card preview (21)
What is an exothermic reaction?
A reaction that releases energy to the surroundings (temperature increases)
What is an endothermic reaction?
A reaction that absorbs energy from the surroundings (temperature decreases)
Give two examples of exothermic reactions.
Combustion Neutralisation
Give two examples of endothermic reactions.
Thermal decomposition Reaction between citric acid and sodium hydrogencarbonate
What is activation energy?
A: The minimum amount of energy needed for a reaction to start
Q: How can you tell if a reaction is exothermic on an energy profile diagram?
A: The products are lower in energy than the reactants
Q: How can you tell if a reaction is endothermic on an energy profile diagram?
A: The products are higher in energy than the reactants
What is a reaction profile?
A: A diagram that shows the energy change during a chemical reaction
Q: In a reaction profile, what does the peak represent?
A: The activation energy
Q: What is bond breaking?
A: An endothermic process (requires energy)
Q: What is bond forming?
A: An exothermic process (releases energy)
Q: How do you calculate overall energy change in a reaction?
A: Energy in (breaking bonds) − Energy out (forming bonds)
: If more energy is released making bonds than is used to break them, the reaction is…?
A: Exothermic
What is a simple cell?
A: A system that produces electricity from two different metals in an electrolyte
Q: What affects the voltage of a cell?
A: The difference in reactivity between the two metals
What is a battery?
A: Two or more cells joined together
Why do batteries eventually stop working?
The reactants run out and the reactions can’t be reversed
What is a fuel cell?
A cell that combines a fuel (like hydrogen) with oxygen to produce electricity
What are the advantages of hydrogen fuel cells?
Don’t produce pollutants Lightweight and compact Constant supply of electricity
: What are the disadvantages of hydrogen fuel cells?
Hydrogen is flammable Hard to store Often made using non-renewable energy
What are the half equations in a hydrogen fuel cell?
At cathode: O₂ + 4H⁺ + 4e⁻ → 2H₂O At anode: H₂ → 2H⁺ + 2e⁻