Energy changes Flashcards
Define an endothermic change
An endothermic change is a change in which heat is absorbed from the surroundings
Define an exothermic change
An exothermic change is a change in which heat is released
Is condensation endothermic or exothermic
Exothermic
What are some exothermic chemical reactions
- Combustion of fuels
- Neutralisation reaction
- Reaction of acid and metal
- Respiration
Is freezing endothermic or exothermic
Exothermic
Is melting endothermic or exothermic
Endothermic
What are some endothermic chemical reactions
- Thermal decomposition
- Photosynthesis
Describe what happens to bonds in an endothermic change
Bonds break as heat is absorbed
Describe what happens to bonds in an exothermic change
Bonds form as heat is released
Why is the enthalpy change positive
- Energy level of products is higher than that of reactants
- Energy released during bond forming in products is less that energy absorbed during bond breaking in reactants
- Reaction is endothermic
Define enthalpy change
Enthalpy change is the overall heat change in a reaction
Why is the enthalpy change negative
- Energy level of products is lower than that of reactants
- Energy released during bond forming in products is more than energy absorbed during bond breaking in reactants
- Reaction is exothermic
Define activation energy
Activation energy is the minimum amount of energy that reacting particles must possess in order for chemical reaction to occur
Define bond energy
Bond energy is the energy absorbed to break one mole of covalent bonds, and is measures in kJ/mol
Summarise what is an exothermic change
- Heat is released
- Temperature of substance increases
- Energy level of products is lower than that of reactants
- Energy released to form bonds in products is higher than energy absorbed to break bonds in reactants
- Enthalpy change is negative
