8. Energy Changes Flashcards
Exothermic Change
Definition + Temp. change + Energy level of products & reactants + ∆H
Exothermic change is a change in which heat is given out/released to the surroundings.
There is an increase in the temperature of the mixture.
The energy level of products is lower than the energy level of reactants.
Enthalpy change is negative.
Endothermic Change
Definition + Temp. change + Energy level of products & reactants + ∆H
Endothermic change is a change in which heat is taken in/absorbed from the surroundings.
There is a decrease in the temperature of the mixture.
The energy level of products is higher than the energy level of reactants.
Enthalpy change is positive.
Exothermic Physical Changes
- Condensation
- Freezing
- Crystallisation
- Deposition
- Dilution of acids and alkali
- Dissolution of sodium hydroxide (NaOH)
Endothermic Physical Changes
- Evaporation
- Boiling
- Melting
- Sublimation
- Dissolution of ammonium chloride (NH4Cl)
Exothermic Chemical Reactions
- Combustion of fuels
- Neutralisation
- Reactions of acid with metals
- Respiration
Endothermic Chemical Reactions
- Thermal decomposition of compounds
- Photosynthesis
Explain, in terms of bond breaking and bond forming, why the reaction is exothermic.
The reaction is exothermic because the energy given out/released during bond forming in products is more than the energy taken in/absorbed during bond breaking in reactants.
Explain, in terms of bond breaking and bond forming, why the reaction is endothermic.
The reaction is endothermic because the energy given out/released during bond forming in products is less than the energy taken in/absorbed during bond breaking in reactants.
Bond Energy
Definition
Bond energy is the energy absorbed to break one mole of covalent bonds.
Measured in kJ/mol
Activation Energy
Definition
Activation energy is the minimum amount of energy that reacting particles must possess in order for a chemical reaction to occur.
Symbol: Ea & Measured in kJ
