# Chemistry

Discussion in 'DAT Discussions' started by Kami, Apr 6, 2007.

1. ### Kami Member

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OK so I have come up with a hyopthetical question relating to Le chatteliers principle which I made up by myself and here it is:

2A + 3B ------> 4C + 5D delta H= 20 kcal

The questions are as follows:

a) what will be the direction of the equilibrium if the temperature is increased and why?
b) what will be the direction of the equilibrium if the temperature is decreased and why?
c) what if the pressure is reduced and the volume is increased then which direction will the equilibrium go and why?
d) what if the pressure is increased and the volume is reduced then which direction will the equilibrim go and why?

3. ### Streetwolf Ultra Senior Member Dentist

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a) Since delta H is positive it's endothermic and you need to add heat to make the reaction go to completion. In a sense, heat is a reactant. So since you are adding a 'reactant', the equilibrium shifts right.
b) Temperature decreased means a 'reactant' would be reduced, so equilibrium shifts left.
c) I'm assuming they are all gases... Since there are 9 moles on the right and 5 on the left, reducing pressure would shift it right. Increasing volume means more room, and this would also shift it right.
d) Increasing pressure shifts it left. Decreasing volume shifts it left (less room, so the reactants would be favored since there are fewer moles of them).

4. ### Kami Member

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So what that means is that in an endothermic reaction an increase in temperature will lead to production of greater number of moles and in this reaction its the right whereas decreased temperature leads to the production of fewer number of moles and therefore its left. A similar example that I can think of is A+B ---->C + heat.
So an increase in temperature will lead to the production the side that has greater number of moles and therefore more A and B whereas a decrease in temperature will lead to production of the side that has fewer moles which is C. The process is reversed if its an exothermic reaction. Is this correct?

5. ### Streetwolf Ultra Senior Member Dentist

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If you have A + B --> C and you add A or you add B (or both), it shifts to the right. If you add C it shifts left. If you take away A, B, or both, it shifts left. If you take away C, it shifts right.

If it's endothermic, heat is like a reactant. So you have A + B + heat --> C. You treat heat as though it's a normal reactant. If you add A or B or heat or any combo, it shifts right. If you take away A, B, heat, or any combo, it shifts left.

If it's exothermic, heat acts like a product. You'd have A + B --> C + heat. Same rules apply. Pretend that instead of the above equation you have A + B --> C + D, where D represents heat.

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