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# Chemistry AS Help - Kc Equilibrium Question watch

1. Can anyone help with this equilibrium Kc question ?!?

Kc of a reaction is 6.40x10^-2

The reaction was repeated at a higher temperature. The equilibrium constant was determined to be 2.1x10^-3.

Deduce with reason whether the forward reaction is exothermic or endothermic?
2. (Original post by JulieWaters)
Can anyone help with this equilibrium Kc question ?!?

Kc of a reaction is 6.40x10^-2

The reaction was repeated at a higher temperature. The equilibrium constant was determined to be 2.1x10^-3.

Deduce with reason whether the forward reaction is exothermic or endothermic?
For any reaction,

Where A and B are your reactants and C and D are your products.

Now, your Kc value has decreased.
How do you decrease the value of a fraction?

You can either increase the denominator, or decrease the numerator, or do both.
For instance,
I've increased the denominator from 3 to 5.

Therefore, at this higher temperature, you had more reactants, and/or less products.

A +B C + D

Therefore, the equilibrium must be shifting to the left.
We are told that this Kc value is given at a higher temperature. Le Chatelier's Principle tells us that the equilbrium shifts to oppose the change. Therefore, the equilbrium is shifting to the left because it decreases the temperature, i.e. it is endothermic.

If the reverse reaction is endothermic, it must mean the forward reaction is exothermic.
Spoiler:
Show
I feel like I'm dillydallying too much but I just wanted to make sure it was understood well.
3. (Original post by RMNDK)
For any reaction,

Where A and B are your reactants and C and D are your products.

Now, your Kc value has decreased.
How do you decrease the value of a fraction?

You can either increase the denominator, or decrease the numerator, or do both.
For instance,
I've increased the denominator from 3 to 5.

Therefore, at this higher temperature, you had more reactants, and/or less products.

A +B C + D

Therefore, the equilibrium must be shifting to the left.
We are told that this Kc value is given at a higher temperature. Le Chatelier's Principle tells us that the equilbrium shifts to oppose the change. Therefore, the equilbrium is shifting to the left because it decreases the temperature, i.e. it is endothermic.

If the reverse reaction is endothermic, it must mean the forward reaction is exothermic.
Spoiler:
Show
I feel like I'm dillydallying too much but I just wanted to make sure it was understood well.
Thank you very much! Very well explained !

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Updated: February 21, 2016
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