Predict the direction of the net reaction in each of the following system, as a result of increasing the temperature. Delta H is an indicator or whether the reaction releases heat delta H(-), or heat is absorb delta H(+). Write where the direction shifts.
a)3O2(g)=2O3(g) H=+284kJ
b)2SO3(g)+O2=2SO5(g) H=-198.2kJ
c) 2H2O(g)=2H2(g)+O2 H=+584kJ
Le Chatelier's Principle says, in simple language, a system in equilibrium will try to undo what we do to it.
for a.
The +284 means the system is endothermic which means the system absorbs energy as it reacts from left to right. So, if we increase heat, the system will try to use up the added heat. How can it do that? The only way (you have only three choices in these problems--shift to right, shift to left, no change) it can do that is to react to produce more products (shift to the right). I find it helpful on problems where heat is indicated with a delta value to rewrite the equation. For a that will be
3O2(g) + heat ==> 2O3(g) I think it makes it easier to see that shifting to the right is using up the heat.
For one with a -delta H, (b for example) I would write it this way.
2SO3(g) + O2(g) ==> 2SO5(g) + heat. By the way, b is not balanced.
To predict the direction of the net reaction in each system as the temperature increases, you need to consider the sign of delta H (enthalpy change) for each reaction. The sign of delta H (+ or -) indicates whether the reaction is exothermic or endothermic, respectively.
a) For the reaction 3O2(g) -> 2O3(g), where delta H = +284 kJ:
Since delta H is positive (+), it means the reaction is endothermic (heat is absorbed). Increasing the temperature would shift the equilibrium towards the products (right side) to absorb more heat and counteract the temperature increase. Therefore, the direction of the reaction would shift to the right.
b) For the reaction 2SO3(g) + O2 -> 2SO5(g), where delta H = -198.2 kJ:
In this case, delta H is negative (-), indicating an exothermic reaction (heat is released). If the temperature is increased, the equilibrium would shift towards the reactants (left side) to absorb the excess heat. Therefore, the direction of the reaction would shift to the left.
c) For the reaction 2H2O(g) -> 2H2(g) + O2, where delta H = +584 kJ:
Since delta H is positive (+), it suggests an endothermic reaction (heat is absorbed). If the temperature is increased, the equilibrium would shift towards the products (right side) to absorb more heat. Consequently, the direction of the reaction would shift to the right.