For the chemical reaction shown below, select the best answer.

Question

H2 + O2 + Br2 ----> HBrO

A. some energy will be released and some energy will be absorbed with the reaction occurs, but more energy will be absorbed than will be released

B. some energy will be released and some energy will be absorbed with the reaction occurs, but without knowing more information than what is given here, we cannot predict whether overall energy will be released or will be absorbed

C. energy will be released while the chemical reaction occurs

D. some energy will be released and some energy will be absorbed with the reaction occurs, but more energy will be released than will be absorbed

E. energy will be absorbed while the chemical reaction occurs

Answer 1

H2 + O2 + Br2 ----> 2HBrO
The choices are a little confusing with the wording; i.e., it makes more sense to use "when" instead of "with". For example, I think it makes more sense for the first choice to read as follows: some energy will be released and some energy will be absorbed WHEN the reaction occurs, but more energy will be absorbed than will be released. The other choices have the same wording problem in my opinion. Here is the way to answer the problem. By the way, I couldn't find the delta Go formation for HBrO but I did find pKa for HBrO. pKa is about 8 which makes Ka about 1E-8. Using dGo = -RTlnK give us a negative value for dGo formation @ 298 K.
Recall that delta Grxn = (n*dGo formation of products) - (n*Go formation of reactants). WHEN the reaction occurs, we know that dGo for HBrO will be negative. Also we know that dGo for H2, O2, and Br2 in the elemental state are zero; therefore, dGo rxn must be negative and that means energy is released. Knowing energy is released in the reaction should give you the tool the choose the correct answer to the problem. Post your thinking if you get stuck.