SC19 Flashcards
(15 cards)
What is enthalpy?
Energy.
How can chemical reactions be described?
- Exothermic (ΔH = -ve)
- Endothermic (ΔH = +ve)
Which reactions are always exothermic?
- Neutralisation
- Combustion (reaction with oxygen)
What is an exothermic reaction?
A reaction that gives out heat energy.
What happens during an exothermic reaction?
Temperature of the reaction mixture and the surroundings increases.
What are examples of exothermic reactions?
- Combustion - burning
- Neutralisation
- Rusting of iron
- Hot packs
What is an endothermic reaction?
A reaction that takes in heat energy.
What happens during an endothermic reaction?
Temperature of the reaction mixture and the surroundings decreases.
What are examples of endothermic reactions?
- Photosynthesis
- Melting ice cubes
- Evaporating liquid water
- Dissolving ammonium chloride in water
- Cold packs
What is the difference in purpose of energy level diagrams and energy profile diagrams?
Both are used to model energy change during a chemical reaction.
In energy level diagrams, energy stored in bonds is represented as a horizontal line - the greater the energy stored, the higher the line.
Energy profile diagrams differ because they show activation energy (minimum amount of energy needed by colliding particles for reaction to occur).
Check teacher notes SC19 slide 9.
What chemical reaction is associated with bond-breaking?
Bond-breaking is an endothermic process since it takes in energy.
What chemical reaction is associated with bond-making?
Bond-making is an exothermic process since it releases energy.
When is a reaction exothermic?
When more energy is released when the bonds of the products are formed than the energy taken in to break the bonds of the reactants.
When is a reaction endothermic?
When more energy is taken in to break the bonds of the reactants than the energy released when the bonds of the products are formed.
How do we calculate energy/enthalpy change?
Energy change = bond energies of reactants - bond energies of products
