### Enthalpy and Entropy - Chemistry LibreTexts

Thermodynamic Property Relations for Single Phase Systems. Apart from internal . Relations for Enthalpy, Entropy and Internal Energy. One may. we'll study free energy (G) and its relationship to enthalpy, entropy and The second property is the measure of entropy (S), which is a. internal energy, heat, work, PV diagrams, enthalpy, Hess's law, entropy, and Gibbs free energy. More rigorous Gibbs free energy / spontaneity relationship.

### The Difference Between Entropy and Enthalpy in Thermodynamics

Spontaneity is the direction in which the reaction will take place without outside interference. In other words, it doesn't need us to keep putting in work or energy to keep it happening.

The Gibbs free energy equation we will be working with is Delta or change in G is equal to change in enthalpy minus temperature multiplied by the change in entropy. This is a very important equation for you to remember, so be sure to commit it to memory.

G equals H minus TS.

### Energy, Enthalpy, and the First Law of Thermodynamics

Enthalpy and Entropy Revisited As we can see from our equation, Gibbs free energy is calculated from the changes in enthalpy and entropy, as well as the temperature at which the reaction is carried out at. Let us quickly remind ourselves about these important thermodynamic quantities.

Enthalpy H is a measure of how much energy is released or absorbed during a chemical reaction. Energy, in the form of heat, is released in an exothermic reaction, and the change in enthalpy is negative, -H.

The second property is the measure of entropy Swhich is a measure of disorder or randomness in the system. Why Are Reactions Spontaneous? Now it turns out that for a spontaneous reaction, the sign of Delta G must be negative.

Knowing this, what effect does enthalpy and entropy have on spontaneity? Let us first look at enthalpy: And now, let's look at entropy: The Effect of Temperature Got it?

## The Difference Between Entropy and Enthalpy in Thermodynamics

Now, if only it were that simple! Let me throw a wrench in the works. We know from everyday experience that water freezes spontaneously, and we recall that solid ice is more ordered than liquid and so the entropy of the system has gone down.

The Delta S term is negative, so why is this reaction spontaneous? I can hear you shouting at the video, but it has to be at freezing temperature for this to happen.

Mathematically, we can look at the change in energy of a system as being a function of both heat and work: If q is negative, then the reaction is exothermic, that is, heat is given off to the external surroundings. You might also remember the terms kinetic energy and potential energy.

Kinetic energy is the energy of motion -- the amount of energy in an object that is moving.

Potential energy is stationary, stored energy. If you think of a ball sitting on the edge of a table, it has potential energy in the energy possible if it falls off the table. Potential energy can be transformed into kinetic energy if and when the ball actually rolls off the table and is in motion.

The total energy of the system is defined as the sum of kinetic and potential energies. In descriptions of the energy of a system, you will also see the phrase "state properties". A state property is a quantity whose value is independent of the past history of the substance.

Typical state properties are altitude, pressure, volume, temperature, and internal energy. Enthalpy Enthalpy is an interesting concept: