Question

For a spontaneous process at constant temperature and pressure, the change in Gibbs free energy ($\Delta G$) is

• A. Negative
• B. Positive
• C. Zero
• D. Infinite

Hint:

Remember that for any spontaneous process under standard conditions of constant temperature and pressure, $\Delta G < 0$.

Answer 1

The Correct Option is A

Step 1: Meet Gibbs free energy.
Gibbs free energy change $\Delta G$ tells us if a change can happen on its own at fixed temperature and pressure. Its sign is the key.
Step 2: State the rule.
The rule is simple. If $\Delta G$ is less than zero the process is spontaneous. If $\Delta G$ is more than zero it cannot happen on its own. If $\Delta G$ is zero the system is at balance.
Step 3: Write the formula.
We use\[ \Delta G = \Delta H - T\Delta S \]Here $\Delta H$ is heat change and $\Delta S$ is disorder change.
Step 4: Link to useful work.
A negative $\Delta G$ means the system can release energy to do useful work. That is why such a change runs by itself.
Step 5: Check the wrong options.
A positive value means the change needs a push from outside, so it is not spontaneous. A zero value is only the balance point. Infinite has no meaning here.
Step 6: Final choice.
So for a spontaneous change $\Delta G$ must be negative.\[ \boxed{\Delta G < 0\ \text{(Negative)}} \]