Chem Equilibrium Pt.4 Post-Assess

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Anna Yakura 2F
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Chem Equilibrium Pt.4 Post-Assess

Postby Anna Yakura 2F » Mon Jan 04, 2021 12:01 pm

Hello, I'm having trouble with this question in the chemical equilibrium pt.4 post-assessment.

Predict the shift in equilibrium position, if any, which will occur when the temperature is increased. The hydrolysis of ATP:
ATP (aq) + H2O (l) ⇌ ADP + PO42-(aq) delta H° = -30 kJ.mol-1

I know that the reaction is endothermic because of the negative H, but don't know what to do from there.

Kareena Patel 1G
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Re: Chem Equilibrium Pt.4 Post-Assess

Postby Kareena Patel 1G » Mon Jan 04, 2021 12:10 pm

This reaction would actually be exothermic because H is negative. If H is negative, it is exothermic and therefore heat is released as a product. If H is positive, it is endothermic and heat is added as a reactant. So for this problem, if the temperature increased, since it is exothermic, the reaction will shift towards the reactants since heat is a product.

Ria Nawathe 1C
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Re: Chem Equilibrium Pt.4 Post-Assess

Postby Ria Nawathe 1C » Mon Jan 04, 2021 12:24 pm

Hi! Like the previous response stated, a negative delta H indicates an exothermic reaction, as heat is being released/lost from the reaction system. You would consider the heat that is released to be a product of the reaction. Therefore, if temperature is increased, you are essentially increasing a component on the product side, so Le Chatlier's Principle tells you that there will be a shift in the opposite direction towards the reactants.

Akash J 1J
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Re: Chem Equilibrium Pt.4 Post-Assess

Postby Akash J 1J » Mon Jan 04, 2021 12:30 pm

Hello, when trying to determine whether a rxn is exo/endothermic, it is easiest to look at the sign on the delta H value. In this case, since it is negative, the rxn is exothermic. Remember, delta H is (enthalpy of products) - (enthalpy of reactants). When it is (-), the reactants have a greater enthalpy than the reactants, so energy is given off by the rxn.

Now, you can write "heat" as a product because it is given off by the rxn. You can now apply the normal rules, so in this case, by increasing the temperature, you are "increasing the amount of product" so the overall equilibrium must shift towards the formation of products.

Hope this helps.

Arezo Ahmadi 3J
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Re: Chem Equilibrium Pt.4 Post-Assess

Postby Arezo Ahmadi 3J » Mon Jan 04, 2021 12:37 pm

Anytime that the given heat is negative, you would identify this as an exothermic reaction because heat is being given off. Thus, if heat is being given off, or produced, this means that heat is a product. An increase in the products means that to return to equilibrium, a shift to the left, or a shift to the reactants is favored.

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