Problem 43 - Chemistry: An Atoms-Focused Approach

Question

How do we calculate the overall free-energy change of a process consisting of two steps?

Step-by-Step Solution

Answer

Answer: To determine the overall free-energy change of a process consisting of two steps, you need to first calculate the free-energy change for each individual step using the equation ∆G = ∆H - T∆S. Then, add the individual free-energy changes of both steps to find the overall free-energy change: ∆G_total = ∆G_step1 + ∆G_step2. Interpret the overall free-energy change to determine whether the process is spontaneous, non-spontaneous, or near equilibrium.

Step 1: Understanding free-energy change

Free-energy change (∆G) is a measure of the maximum amount of reversible work that a thermodynamic system can perform during a process. It helps us determine whether a process, such as a chemical reaction, will occur spontaneously or not. If ∆G is negative, the process is spontaneous, while if ∆G is positive, the process is non-spontaneous.

Step 2: Calculating free-energy change for individual steps

In order to determine the overall free-energy change of a process consisting of two steps, we first need to calculate the free-energy change for each individual step. This can be calculated using the equation: ∆G = ∆H - T∆S Here, ∆G is the free-energy change, ∆H is the change in enthalpy (heat) of the system, T is the temperature in Kelvin, and ∆S is the change in entropy (disorder) of the system. Ensure that you have the required data for each individual step, such as enthalpy change, temperature, and entropy change.

Step 3: Combining the free-energy changes of the two steps

Once the free-energy change is calculated for both steps, determine the overall free-energy change of the process consisting of these two steps by adding their individual free-energy changes: ∆G_total = ∆G_step1 + ∆G_step2 This will give you the overall free-energy change for the entire process.

Step 4: Interpreting the overall free-energy change

Finally, interpret the obtained overall free-energy change to determine whether the process will occur spontaneously or not. If the overall free-energy change (∆G_total) is negative, the process is spontaneous, and if it is positive, the process is non-spontaneous. If the overall free-energy change is close to zero, the process may be near equilibrium.