Predict whether the following reactions would be spontaneous or not under standard conditions or if it's impossible to tell.
2 KClO3(s) + 3 C(s) --> 3CO2(g) + 2KCl(s) Exothermic
2 NO(g) + O2(g) --> 2NO2(g)
Exothermic
H2(g) + Zn(ClO3)2(s) --> 2HClO3(l) + Zn(s) Endothermic
I'm having trouble in trying to figure out if they are spontaneous or not. I understand that if it's exothermic, they are usually spontaneous, but with the given data, I am just unsure.
That is right about delta H. The problem is that no data are given for delta S. You can guess about delta S, however, and be close usually. For example, #1: you have solids on the left (reactants) and gas on the right so delta S must be + (more disorder in gases than solids) so we would guess with dH - and dS +, dG would be - and reaction spontaneous. Do 2 and 3 the same way. 2 you have 3 mols gases going to 2 of gases so dS is -. #3 you have gas on left goig tro liquid on right. dS will be -.
I have a question about the format of the problem itself. So it's asking to predict whether the reactions are spontaneous or not, so should I just write spontaneous/non spontaneous, or write that with an explanation?
I don't know the instructions given. If the instructions suggest an explanation then you should giver one; otherwise, I would just write spontaneous or non-spontaneous.
Coolio! Thanks for the help Doc!
To determine whether a reaction is spontaneous or not, you can use a combination of two factors: the change in free energy (∆G) and the reaction's equilibrium constant (K).
1. For a reaction to be spontaneous under standard conditions (∆G° < 0), the reaction must have a negative standard free energy change (∆G°). In other words, the products are more stable than the reactants.
2. If the reaction is exothermic, it means it releases energy into the surroundings. Exothermic reactions generally have negative ∆G° values, making them more likely to be spontaneous.
Keeping these factors in mind, let's analyze each reaction:
1. 2 KClO3(s) + 3 C(s) -> 3 CO2(g) + 2 KCl(s) - Exothermic
Without specific values for ∆G° or K, it is impossible to determine the spontaneity of this reaction. However, since the reaction is exothermic, there is a higher likelihood of it being spontaneous.
2. 2 NO(g) + O2(g) -> 2 NO2(g) - Exothermic
Similar to the previous reaction, without specific values for ∆G° or K, we cannot determine the spontaneity with certainty. However, it is worth noting that the formation of NO2 from NO and O2 is often an exothermic reaction and tends to be spontaneous.
3. H2(g) + Zn(ClO3)2(s) -> 2 HClO3(l) + Zn(s) - Endothermic
Endothermic reactions generally have positive ∆G° values, which implies they are non-spontaneous under standard conditions. However, in this case, the presence of a solid reactant (Zn(ClO3)2) can affect the equilibrium. To determine the spontaneity, you need to know the value of the equilibrium constant (K) and compare it to 1.
In summary:
- The first two reactions, being exothermic, have a higher likelihood of being spontaneous.
- The last reaction, being endothermic, is non-spontaneous under standard conditions, but you need the value of K to make a definite determination.
Remember that having specific values for ∆G° or K is essential for making accurate assessments of spontaneity.