Final answer:
To change the sign of ΔG of a reaction, one can alter the temperature, enthalpy, or entropy of the reaction. This aligns with the Gibbs free energy equation ΔG=ΔH-TΔS. Adding a catalyst does not change ΔG as it does not affect these states.
Step-by-step explanation:
To change the sign of ΔG of a reaction, we can look at the Gibbs free energy equation, which is ΔG=ΔH-TΔS. This equation shows that the sign of ΔG can change due to changes in the reaction's enthalpy (ΔH), entropy (ΔS), or temperature (T).
Answer A) Changing the temperature can affect ΔG, especially if the reaction has positive ΔS. An increase in temperature will amplify the TΔS term, potentially making ΔG more negative for endothermic reactions with positive ΔS.
Answer B) Changing the enthalpy (ΔH) of a reaction will directly impact the ΔG value. A decrease in ΔH will make ΔG more negative, and an increase in ΔH will do the opposite.
Answer C) Changing the entropy (ΔS) will also change ΔG. Greater disorder (positive ΔS) in a reaction tends to drive ΔG to be more negative, particularly when multiplied by T in the equation.
Answer D) Adding a catalyst to a reaction reduces the activation energy, making the reaction proceed faster. However, it does not change the ΔG of the reaction, as it does not affect the enthalpy, entropy, or temperature of the system.
Therefore, the correct answers to changing the sign of ΔG of a reaction are to change the temperature (A), change the enthalpy (B), or change the entropy (C).