Consider the system I2 (g) <----> 2I (g) with H=+151 KJ. Suppose the system is at equilibrum at 1000 degree celsius. In which way will the reaction occur under each of the following conditions?

1. 1 atoms are added?
2. The temperture is increased?
3. The temperature is decreased?
4. The system is compressed?

It won't do any good for me to give you the answers. First, let's write the equation.

I2(g) + heat ==> 2I(g)

Now, Le Chatelier's Principle says that the reaction will shift so as to undo what is done to it.
1. I atoms are added. That increases I on the right, the reaction will want to decrease I (since we added I the reaction will try to undo that). The only way it can do that is to shift away from I which means a shift to the left.

2. T is increased. So the reaction will shift to use up the heat. How can it do that? By shifting to the right (again, away from what we added).

That does 1, 2, (and actually 3, too), Leaves you with 4 to reason through.

Was helpful only that I still wanted the 4th answer

To determine the direction in which the reaction will occur under each of the given conditions, we need to consider the effect of each condition on the reaction.

1. If 1 atom (assuming iodine atom, I) is added:
By adding an iodine atom, the concentration of I atoms will increase, causing an imbalance. According to Le Chatelier's principle, the system will try to counteract this change by shifting the reaction to the left, meaning it will favor the reactants. So, the reaction will occur in the backward direction: 2I (g) -> I2 (g).

2. If the temperature is increased:
If the equilibrium temperature of the system is increased, the system will try to counteract this change by shifting the reaction in the endothermic direction (the direction that absorbs heat). In this case, the reaction is endothermic, meaning it absorbs heat. Therefore, increasing the temperature will favor the forward reaction, which is the heat-absorbing direction. So, the reaction will occur in the forward direction: I2 (g) -> 2I (g).

3. If the temperature is decreased:
Conversely, if the equilibrium temperature of the system is decreased, the system will try to counteract this change by shifting the reaction in the exothermic direction (the direction that releases heat). In this case, the reaction is exothermic, meaning it releases heat. Therefore, decreasing the temperature will favor the reverse reaction, which is the heat-releasing direction. So, the reaction will occur in the backward direction: 2I (g) -> I2 (g).

4. If the system is compressed:
By compressing the system, the volume will decrease. According to Le Chatelier's principle, if the volume of a gaseous system is decreased, the system will try to counteract this change by shifting the equilibrium in the direction that decreases the total number of gaseous moles. In this case, the total number of moles of gas is the same on both sides of the reaction. Therefore, compressing the system will not have any significant effect on the reaction direction.

In summary:
1. 1 atom added: The reaction will occur in the backward direction.
2. Temperature increased: The reaction will occur in the forward direction.
3. Temperature decreased: The reaction will occur in the backward direction.
4. System compressed: No significant effect on the reaction direction.