Equilibria Flashcards
What is a reversible reaction?
Can go forwards or backwards
What would ∆H be in the backwards reaction?
Forwards = N₂ + 3H₂ ⇌ 2NH₃
∆H = -92 KJ/mol
Backwards = 2NH₃ ⇌ N₂ + 3H₂
+92KJ/mol
What are examples of reversible reactions?
Decomposition of NH₄Cl (ammonium chloride)
Dehydration of CuSO₄ * 5H₂O (copper sulphate crystals)
Explain what happens during the decomposition of ammonium chloride
NH₄Cl ⇌ NH₃ + HCl
NH₄Cl (white solid) is heated in testube (promotes forwards reaction)
NH₃ + HCl cools down (promotes backwards reaction)
White solid forms at top of test tube
Explain what happens during Dehydration of copper sulphate crystals
CuSO₄ * 5H₂O ⇌ CuSO₄ + 5H₂O
CuSO₄ * 5H₂O (blue) is heated to promote forwards reaction
H₂O added to CuSO₄ (white) to promote backwards reaction
What are reversible reactions used for?
Haber process: how to make ammonia, used in fertilisers
What is equilibrium?
in a reversible reaction, both forwards and backwards reaction occurs at the same time. It is dynamic
What is dynamic equilibrium?
forwards and backwards reaction occurring at same rate
What happens to the composition of the system?
will not change
(no observational change)
Why is a closed system needed?
stops energy (or reactant/product) from being transferred to/from system
What is Le Chatelier’s principle?
whenever a change in conditions is introduced to a system at equilibrium, the position of equilibrium shifts to try and counter the change
(a system at equilibrium will oppose any change made to it)
What is equilibrium position?
gives an idea of how ratio of reactant:product compares
reactants ⇌ products
what happens if equilibrium moves to left?
more reactant
reactant ⇌ products
what happens if equilibrium moves to right?
more product
What happens if you increase amount of reactant?
equilibrium moves to right as uses up extra reactant, increasing product
What happens if you reduce amount of reactant?
equilibrium moves to left to create more reactant, increasing reactant
What happens if you increase amount of product?
equilibrium moves to left as uses up extra product, increasing reactant
What happens if you reduce amount of product?
equilibrium right as creates more product, increasing product
What happens if you increase pressure?
equilibrium moves to side with less moles of gas, increasing side with less moles of gas
What happens if you decrease pressure?
equilibrium moves to side with more moles of gas, increasing side with more moles of gas
What happens if you increase temperature?
promotes endothermic reaction, equilibrium moves to side which is endothermic
e.g. backwards (left) = endothermic then moves to left side
What happens if you decrease temperature?
promotes exothermic reaction, equilibrium moves to side which is exothermic (to release energy)
What happens if you add a catalyst?
no effect on equilibrium
will achieve equilibrium quicker
N₂O₄ ⇌ 2NO₂
∆H = +58 KJ/mol
forwards = endothermic
What happens if you increase temperature?
What happens if you increase pressure?
increase temp will promote endothermic reaction. Forwards reaction is endothermic so position of equilibrium moves to right, increasing product
increasing pressure moves position of equilibrium to side with less moles of gas which is left, increasing reactant
How can more reactant be made?
reduce amount of reactant / increase product
How can more product be made?
reduce amount of product / increase amount of reactant
