C7 - Energy Changes Flashcards
define exothermic reaction
A reaction that transfers energy to the surroundings
define endothermic reaction
A reaction that takes in energy from the surroundings
give 2 examples of exothermic reactions
- respiration
- combustion
- neutralisation
- oxidation
give 2 examples of endothermic reactions
- photosynthesis
- thermal decomposition
- reduction
What is an energy change represented by?
ΔH
Endothermic or Exothermic?
1. breaking bonds
2. making bonds
- breaking bonds is endothermic
- making bonds is exothermic
Endothermic or Exothermic?
1. positive ΔH
2. negative ΔH
ΔH - energy change
- endothermic because more energy is stored in the products
- exothermic because less energy is stored in the products
define activation energy
the minimum energy required for a reaction to start
What diagram is used to show if a reaction is exothermic or endothermic?
Energy level diagram - potential energy against time
When do reactions occur in terms of particles?
Chemical reactions occur when reacting particles collide and have sufficient kinetic energy.
steps for bond energy calculations
- balance the equation
- draw the displayed formula for all the molecules
- calculate the energy required to break bonds in the reactants, ER
- calculate the energy required to make bonds in the products, EP
- ΔH = ER - EP
What type of reaction occurs in an electrical cell?
A redox reaction - displacement
Write a half equation for the reaction occurring at the negatively charged electrode in a hydrogen-oxygen fuel cell
higher
2H2 + 4OH- → 4H2O + 4e-
Write a half equation for the reaction occurring at the positively charged electrode in a hydrogen-oxygen fuel cell
higher
O2 + 2H2O + 4e- → 4OH-
What does a fuel cell use?
A constant supply of fuels to produce a voltage
