text: An exact answer to how this quantity changes between two states is given by the Zwanzig relation or exponential averaging.
full_question: An exact answer to how this quantity changes between two states is given by the Zwanzig relation or exponential averaging. The change in this quantity between two systems in the same configuration can be approximated with the BAR method. This quantity is equal to negative k times temperature times the logarithm of the partition function. This quantity represents the maximum obtainable work from a reversible process and is equal to the internal energy minus entropy times temperature. For 10 points, name this free energy not named for Gibbs.
first_sentence: An exact answer to how this quantity changes between two states is given by the Zwanzig relation or exponential averaging.