# Doubt while using Le Chatelier's principle [closed]

Consider the following reaction

$$\ce{H2}+\ce{I2}\rightleftharpoons\ce{2HI}$$, for this reaction $$\Delta H_r<0$$

Now suppose I introduce more amount of $$\ce{H2}$$ in it, therefore temperature of system increases as total pressure increases. Now by Le Chatelier's Principle, since concentration of $$\ce{H2}$$ increases , therefore reaction moves in direction where it is consumed i.e. in forward direction as said my book but one thing that troubles me is that when we introduce more $$\ce{H2}$$ the temperature of system increases, therefore reaction should move backward contradicting the fact given in my book.

Where I'm getting confused?

I think that when my book says that equilibrium shifts forward as we introduce more $$\ce{H2}$$, it must also say that temperature of system remains constant.

• For complex changes with more, mutually opposing factors, quantitative evaluation may be needed. But my guess is, the change of reaction quotient has much bigger influence than change of temperature and therefore of equilibrium constant ( see van't Hoff equation Jun 28 at 5:22
• I introduce more amount of $\ce{H2}$ in it, therefore temperature of system increases as total pressure increases. Why do you think that the temperature is increasing? I believe you are missing that $n$ is also changing. Jun 28 at 5:23
• @nisargbhavsar The OP may mean adiabatic compression by injection of hydrogen. Jun 28 at 5:27
• I think in problems with Le Chatelier's Principle we change only one thing and other factors are held constant. In this case, if you want to include more factors at a time, I think more information should be included in the problem. For example, it could be that the reaction is preceding inside a container with a piston, so it's possible to leave temperature constant by increasing the volume (moving the piston). Jun 28 at 6:01
• The principle says temperature increase would push reaction toward left side, while adding a reactant would push the reaction toward right side. It does not say which effect is stronger. You need quantitative computation for that. Jun 28 at 6:49