The following reaction has a positive value of ΔG°.
2H2O(g) → 2H2(g) + O2(g)
Which of the following statements must be true?
A. The reaction is slow.
B. The reaction will not occur. That is, when H2O(g) is introduced into a flask, no O2 or H2 will form
even over a long period of time.
C. The reaction is exothermic.
D. The equilibrium lies far to the right.
E. None of these is true.
Hello, how are you?
The correct answer to this Q is E. but I have chosen B. Could you please explain why all of them cannot be true? Thank you
A. dG has nothing to do with speed of a reaction. Carbon is the more stable form of diamond but all the girls getting diamond rings today need not worry about that ring crumbling tomorrow. :-).
B. All reactions occur to some extent no matter how small. So this has an extremely small Keq, so it's small but still occurs.
C. Is the reaction exothermic. I thought the reverse reaction was exothrmic.
D. No, the eq lies far to the left; otherwise all of our lakes and rivers would have dried up long ago and we would have plenty of oxygen and hydrogen in our atmosphere.
E. That leaves E.
Thank you!
To determine which of the statements is true, we need to understand the relationship between ΔG° and the spontaneity of a reaction.
ΔG° represents the standard Gibbs free energy change, which is an indicator of a reaction's spontaneity. A positive value of ΔG° indicates that the reaction is non-spontaneous under standard conditions (i.e., at 1 atm pressure and 25°C).
Now, let's evaluate each statement:
A. The reaction is slow.
The speed of a reaction is not determined by its ΔG° value. The rate of a reaction depends on other factors such as temperature, concentration, and the presence of catalysts. Therefore, statement A is not necessarily true.
B. The reaction will not occur.
A positive value of ΔG° does not mean that the reaction will not occur. It simply indicates that the reaction is non-spontaneous under standard conditions. However, by manipulating the reaction conditions, such as increasing the temperature or adding a catalyst, the reaction may still occur. Therefore, statement B is not necessarily true.
C. The reaction is exothermic.
The sign of ΔG° does not provide information about whether a reaction is exothermic or endothermic. ΔG° only tells us about the spontaneity of the reaction. Therefore, statement C is not necessarily true.
D. The equilibrium lies far to the right.
A positive value of ΔG° actually suggests that the equilibrium lies far to the left, favoring the reactants. This is because the reaction is non-spontaneous under standard conditions, and the products have a higher Gibbs free energy than the reactants. Therefore, statement D is true.
E. None of these is true.
As we have determined that statement D is true, statement E is incorrect. Therefore, the correct answer is D. "The equilibrium lies far to the right."
Note that while statements A, B, and C are not necessarily true, they may still be possible depending on the specific reaction conditions and other factors not indicated by the ΔG° value alone.