Analogy: If you were in a tub of water that was divided in half (with some holes for water to pass through), and dumped some water out from one side, the water on the other side would flow to the side you dumped water out of.
Like the first example shown, H2 was added to the left side, so it would move to the right. That also means some I is taken away to make HI.
If HI was added on the right, you'd go the opposite direction: shift left
For heat, +ΔH means heat was a part of the left side to make the right side happen (endothermic).
-ΔH means reaction is exothermic; heat is produced along with HI.
You'd think that the reaction is divided in two separate beakers, but in real life the H2, I2, and HI are all in the same beaker!
In this case since ΔH is positive, you can treat heat like a reactant (left side)
When you add heat, you're adding to the left side. Like adding water to the left side, water will flow to the other side to balance both sides out.
The reaction will shift right so more product (HI) is made. You could figure out where the H2 and I2 went to make HI
Decreasing the temperature will have the opposite effect.
For pressure, changing the pressure only works if the sides have an unequal amount of moles.
In this case both sides have the same amount of moles:
1 mol H2 + 1 mol I2 = 2 mol HI
2 mol = 2 mol
There wouldn't be any effect.
Sorry I had a lot to explain, hope this helped
