Lesson 11

• Heat of fusion ((delta) h_fus) is the energy needed to melt a substance. Water’s heat of fusion is 6.01 kJ/mol.

• Heat of vaporization ((delta) h_vap) is the energy needed to vaporize a substance. Water’s heat of fusion is 40.7 kJ/mol.

• The high amount of energy needed to turn liquid water into water vapor is because of the hydrogen bonds holding the water molecules together.

• During phase changes, the temperature of the substance does not increase, but the extra energy is used to disrupt the intermolecular forces of the substance.

• In a heating curve, the steeper the angle, the greater the value for the specific heat.

• To find the amount of energy needed to phase change it:

1. use the formula q = mc(delta)T

2. use the heat of fusion to find the amount of energy needed to change phases. (moles x heat of fusion/vaporization )

3. add the two values together; Make sure they are both in the same measurement.

• If entropy increases, then enthalpy can either increase or decrease.

To determine if a reaction will be spontaneous, you look at the concepts of enthalpy and entropy. A reaction is spontaneous if the change in free energy (ΔG) is negative. This can be assessed using the Gibbs free energy equation:

ΔG = ΔH - TΔS

where ΔH is the change in enthalpy, T is the temperature in Kelvin, and ΔS is the change in entropy. If the enthalpy change is negative (exothermic reaction) and the entropy change is positive, the reaction is likely to be spontaneous. Conversely, if the enthalpy change is positive and entropy change is negative, the reaction is non-spontaneous.