Energy Changes in Chemistry Flashcards
(17 cards)
What are exothermic reactions
reactions which give out heat energy.
Energy change for an exothermic reaction will be negative as it has lost energy to its surroundings
What are endothermic reactions
Reactions which take in heat energy
Energy change for an endothermic reaction will be positive as it has gained energy from its surroundings
What is the activation energy
minimum energy required for a reaction to occur
What is a combustion reaction
When something burns in oxygen. When a fuel burns heat energy is given out
Methane + Oxygen = Carbon Dioxide + Water
CH4 + 2O2 = CO2 + 2H2O
What is a neutralisation reaction
When an acid and an alkali react to form salt and water
E.g.
Hydrochloric acid + sodium hydroxide = Sodium chloride + water
HCl + NaOH = NaCl + H2O
What is a displacement reaction
more reactive metal displaces a less reactive metal from a compound
Iron + Copper Sulphate = Copper + Iron Sulphate
Fe + CuSO4 = Cu + FeSO4
What is rusting
Iron rusts when exposed to air and water to form hydrated iron oxide
Iron + Oxygen + Water = Hydrated iron(III) Oxide
Fe + 3O2 + 4H2O = 2Fe2O3.2H2O
What is Hydration
When water is added to an anhydrous salt it forms the hydrated salt
E.g. anhydrous copper sulphate is white and turns blue when water is present
Anhydrous copper (II) Sulphate + Water = Hydrated Copper (II) Sulphate
CuSO4 + 5H2O = CuSO4.5H2O
What is thermal decomposition
Breakdown of compound using heat
Metal carbonates such as calcium carbonate and copper carbonate thermally decompose to form oxides and carbon dioxide
Metal carbonate = Metal oxide + carbon dioxide
What is breaking bonds
Requires Energy
It is an Endothermic process
What is Making Bonds
Gives out energy
Exothermic process
How can the energy change for a reaction be worked out?
Adding together energy needed to break bonds in reactants with energy given out when bonds are formed
If the energy change is negative what has happened
Lost heat energy
Given out heat
Exothermic
If the energy change is positive what has happened
gained heat energy.
It has taken in heat,
it is endothermic.
What type of reaction is the opposite of hydration
Thermal decomposition reaction
What happens when limestone (calcium carbonate) is heated strongly
Breaks down into calcium oxide and carbon dioxide
calcium carbonate = calcium oxide + carbon dioxide
CaCO3 = CaO + CO2
What happens when Copper Carbonate is heated
Decomposes into copper oxide and carbon dioxide and an obvious colour change is visible
Copper Carbonate = Copper Oxide + Carbon Dioxide
CuCO3 = CuO + CO2
(green) (black)
