Final answer:
More heat is added to gas b compared to gas a because their absolute temperatures are different.
Step-by-step explanation:
In an isothermal expansion, the change in entropy of a gas is given by ΔS = Q/T, where ΔS is the entropy change, Q is the heat added to the gas, and T is the absolute temperature of the gas. Since both gases undergo the same entropy change, their entropy changes are equal, meaning that ΔSa = ΔSb. Substituting the equation for entropy change, we get Qa/Ta = Qb/Tb. Since Tb = 2Ta, we can rearrange the equation to get Qa/Qb = Ta/2Ta = 1/2. Therefore, more heat is added to gas b than gas a.