Question

What is difference between enthalpy, entropy, and Gibbs free energy?

1.What is difference between enthalpy, entropy, and Gibbs free energy?

2.For each of the above, what does it mean if the sign is negative? Positive?

3.Provide any equation (from Ch1-2) what includes enthalpy, entropy, or Gibbs free energy

Answer 1

Enthalpy-

The measure of energy in a thermodynamic system is called enthalpy. Enthalpy is usually measured in either Joules or in Calories. Scientists always measure the change in enthalpy of a system, because a system's total enthalpy can't be directly measured.

Entropy-

Entropy is used to describe the amount of freedom or randomness in a system. In other words, entropy is a measure of the amount of disorder or chaos in a system.

Gibbs free energy-

Gibbs Energy is the maximum (or reversible) work that a thermodynamic system can perform at a constant temperature and pressure. This is also defined as a thermodynamic quantity equal to the enthalpy (of a system or process) minus the product of the entropy and the absolute temperature.

b) A negative enthalpy represents an exothermic reaction, releasing heat.

Negative entropy means the system is being compared to its previous state or with other system having a more ordered state than our system. One can not look at a system at any state and tell that the entropy is negative for this particular state.

Negative gibbs free energy means that the reaction is spontaneous in nature and do not require any external energy in order to occur.

c) 3 equations involving the above mentioned quantities in order,

Enhalpy, H, equals the sum of the internal energy, E, and the product of the pressure, P, and volume, V, of the system:

H = E + PV.

To write Entropy, Q is the heat absorbed, T is the temperature, and S is the entropy.

Entropy , S = $\Delta$Q / T

For Gibbs free energy,

ΔG=ΔH−TΔS

where ΔH is the enthalpy change (the heat of the reaction) and ΔS is the change in entropy.