C3.1 chemical reactions Flashcards
Define exothermic
Reaction that releases energy in heat
Define endothermic
A reaction that absorbs heat energy
Define molecule
Two or more atoms covalently bonded
Activation energy
The minimum amount of energy needed to react
Bond energy
Energy needed to break a bond
How to calculate bond energy
- How many bonds there are x bond energy
- reactants will be positive and products will be negative
- mesured in kJ
How to calculate the energy change
Energy needed to break bonds subtract energy released when bonds are made
Why reactions are exothermic or endothermic using energy profiles
Exothermic=When energy released is greater than activation energy
Endothermic= When energy needed to break bonds is greater than energy released
Acid
pH below 7 Form hydrogen ions H+
Alkali
pH above 7 From hydroxide ions OH-
Neutralisation
The reaction between an acid and alkali to form a salt plus water H+ +OH- -> H2O
Acid plus metal
ACID + METAL → SALT + HYDROGEN sulfuric acid + magnesium→ magnesium sulfate + hydrogen H2SO4 + Mg → MgSO4 + H2
ACID + METAL CARBONATE
- ACID + METAL CARBONATE → SALT + CARBON DIOXIDE + WATER
- sulfuric acid + calcium carbonate → calcium sulfate + CO2 + water
- H2SO4 + CaCO3 → CaSO4 + CO2 + H2O
ACID + BASE → SALT + WATER
- ACID + BASE → SALT + WATER
- nitric acid + copper oxide → copper nitrate + water
- 2HNO3 + CuO → Cu(NO3)2 + H2O
Strong acids
Completely ionised and aqueous solutions
Weak acids
Only partially ionised and aqueous solutions
How could you measure the acidity or alkalinity of a substance
Universal indicator or a ph probe
What an exothermic energy profile looks like
What an endothermic energy profile looks like
Examples of exothermic reactions
- Iron rusting
- combustion reaction
- Neutralisation reaction
Endothermic reaction examples
- Photosynthesis
- Cooking an egg
- dissolving salt in water
