Question

[Hye]

State whether the equilibrium constants for each of the following would be increased, decreased or unchanged by a rise in temperature:
   2NH3(g) ->(reverse arrow) N2(g) + 3H2(g);  ΔH = +91 kJ mol–1

Is there any working out (calculations) for this question?

Thanks

[Hye]

Sorry just realised i posted this in the wrong section --'. Mod pls move.

[_avO]

There's no working out, simply memory, or logic

As the question states that the equation is endothermic (Enthalpy of a positive value), it indicates the absorption of energy.
Think of these types of questions with an analogy

Analogy: The water tanks
Think of two water tanks, one as the reactants, one as the products.
A siphoning pipe is placed between both tanks, keeping water levels at equilibrium.

Now back to the equation. Endothermic = absorption of energy
You can (to help you) place the ΔH = +91 on the left, indicating the use of heat.

By increasing the temperature, you are ADDING more heat
By adding more heat (heat is now a reactant) you are "filling" the tank with water.

Which way will the water travel to reestablish equilibrium?
Of course it will be siphoned to the right.

You can use this simple analogy for temperature and concentration.

[crayolé]

There's no working out, simply memory, or logic

As the question states that the equation is endothermic (Enthalpy of a positive value), it indicates the absorption of energy.
Think of these types of questions with an analogy

Analogy: The water tanks
Think of two water tanks, one as the reactants, one as the products.
A siphoning pipe is placed between both tanks, keeping water levels at equilibrium.

Now back to the equation. Endothermic = absorption of energy
You can (to help you) place the ΔH = +91 on the left, indicating the use of heat.

By increasing the temperature, you are ADDING more heat
By adding more heat (heat is now a reactant) you are "filling" the tank with water.

Which way will the water travel to reestablish equilibrium?
Of course it will be siphoned to the right.

You can use this simple analogy for temperature and concentration.

That sounds like a brilliant analogy but could you re-explain it?
I dont completely get it :/

[_avO]

A siphoning pipe placed at the bottom of both tanks will allow water to transfer from one tank to the other, allowing both to be balanced and hence the levels are at an equilibrium

[vexx]

Basically you just need to know that;

For endothermic reactions (ΔH=+) when you increase the temperature the system must act so it reduces the heat, so it increases the forward reaction as energy is being absorbed and this reduces heat, and so increases the eq constant, for the higher the constant, the more the reaction is in the forward direction.