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### question from module

Posted: Tue Jan 15, 2019 1:26 pm
13. State whether the equilibrium shifts towards products, reactants, or neither when the given change occurs.
2 HI(g) + Cl2(g) ⇌ 2 HCl(g) + I2(s) delta H° = -238.0 kJ.mol-1
i. The volume of the system is compressed.
ii. The temperature of the system is decreased.

Can someone explain the answer to this question?

### Re: question from module

Posted: Tue Jan 15, 2019 1:39 pm
When the volume of a system is compressed, the effect on the system depends on how many moles are on each side of the equation. If the moles of the reactants equal the moles of the products, like in this situation, the change in volume has an equal effect on the reactants and the products. Thus, the system remains in equilibrium and does not shift in either direction.

Given that the delta H is negative, we know that this reaction is an exothermic one. Lowering the temperature favors the forward reaction and the reaction shifts towards the products.

### Re: question from module

Posted: Tue Jan 15, 2019 6:32 pm
Same number of moles, so no change in direction of equilibrium!
And temperature is as explained above.

### Re: question from module

Posted: Wed Jan 16, 2019 2:45 pm
Something that helps me with temperature shift is that when it's a negative delta h, you can think of there being a product of heat (+heat on the product side) and when delta h is positive then there is +heat on the reactant side. Thus, if temperature is decreased, then equilibrium would shift to where heat is in the equation: the products.

### Re: question from module

Posted: Wed Jan 16, 2019 5:00 pm
When the volume of the container is decreased, the pressure in the container is therefore increased. This increase in the pressure will cause the reaction to shift towards the side of the chemical equation with fewer moles of gas. Therefore, the equation will shift towards the products. When the temperature of the system is decreased, the equation will shift towards the side which requires the temperature input to proceed. Therefore, the reaction will again shift to the products.