Question

give the SI unit of gibbs energy and standard gibbs energy ??
hurry plz fast ​

Answer 1

Answer:

We can use ΔStotal to predict the direction of a reaction, but largely for historical reasons chemists prefer to think in terms of energy.

ΔStotal = ΔSsystem + ΔSsurroundings

but remember

ΔSsurroundings = -ΔH / T

so,

ΔStotal = ΔSsystem + ( -ΔH / T)

If we multiply through by -T, we get

-TΔStotal = ΔH - TΔSsystem

Since entropy has units of J K-1 mol-1, T x ΔS has units of J mol-1 and is a measure of energy. We call the term '-TΔStotal' the Gibbs free energy after the American chemist Josiah Willard Gibbs. It is given the symbol ΔG so

ΔG = ΔH - TΔSsystem

Notice that if ΔG is negative, the reaction is feasible. Notice also that all the terms in the expression relate to the system rather than the surroundings. This is what makes this quantity so useful to chemists. It is also an energy term, which is a concept more familiar to most chemists than entropy.

Note

We must take care when using mathematical expressions that include both energy and entropy. Chemists normally measure energy (both enthalpy and Gibbs free energy) in kJ mol-1 (kilojoules per mole) but measure entropy in J K-1 mol-1 (joules per kelvin per mole). So it is necessary to convert the units - usually by dividing the entropy values by 1000 so that they are measured in kJ K-1 mol-1.