# Chemistry-Unit 4-Chemical Equilibrium

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What is Kc?
Equlibrium constant
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What is the equation?
Products/Reactants, where each product/reactant is being squared by its number of moles.
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When can this only be used?Why?
At a constant temperature because Kc changes with temperature.
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How to calculate units?
moldm-3/moldm-3 , cancel them out. If left with bottom units then flip (mol-1dm3)
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How to calculate Kc from values? (example)
Put your equation at the top. Put your known conc values before equlibrium on next line (will be 0 for products), then put how much is present in equlibrium (of either products or reactants). Calculate diffrence between the reactant amount at end and
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conc
start, this equals the amount for the products. Make sure its in ratios with their moles. If you have the products in equilibrium then the diffrence = reactants but ratios agian.
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Calculating composition of a mixture (1-x scenario)
At the start we had 1 mol of ethanol and ethanoic acid. The kc is 4, what is the conc of the products? products conc is x and is 1-x (x being how much is used up). Therefore (x)(x)/(1-x)(1-x)= kc. Can then re-arrange to find x.
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Effect of changing temperture on Kc?
Dependant upon whether reaction is exothermic or endothermic. If temp increases and exothermic, kc will decrease (as moves more to left) but if endothermic, it increases.
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why?
Endothermic- increase temp- will move to the right to oppose the increase in temperature. and decrease temp.
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Kc value and position?
Much greater then 1, more towards the right, less then one, over to the left.
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Catalysts?
Have no effect as they increase the rates of both the forward and backward reaction equally.
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If you know the kc of a forward reaction, how to calculate the backward?
1/Kc
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## Other cards in this set

### Card 2

#### Front

What is the equation?

#### Back

Products/Reactants, where each product/reactant is being squared by its number of moles.

### Card 3

#### Front

When can this only be used?Why?

### Card 4

#### Front

How to calculate units?

### Card 5

#### Front

How to calculate Kc from values? (example)