Heat Capacity and Specific Heat
The heat capacity (C) is the amount of heat needed to increase the temperature of a material sample by 1 Co. Mathematically expressed with the following equation:
DQ = C DT
Specific heat (s) is the amount of heat required to raise the temperature of 1 gram of material mass by 1 Co. If we know the specific heat and amount of a substance, the change in temperature of the substance () can express the amount of heat (q) absorbed or released in a chemical reaction.
Information:
q = heat released or absorbed (J)
= temperature change (end - beginning) (0C)
The relationship between heat capacity and heat type is formulated as follows:
Information:
C = heat capacity (J / 0C)
m = sample mass (gr)
c = heat type (J / g0C)
Enthalpy
Enthalpy (H) is the total amount of all forms of energy. The enthalpy (H) of a substance is determined by the amount of energy and all forms of energy possessed by a substance whose amount cannot be measured and will remain constant as long as no energy enters or exits the substance. Kinetic energy is generated because of the atoms and molecules of matter in randomly moving substances. The total amount of all forms of energy is called enthalpy (H). Enthalpy will remain constant as long as there is no energy entering or leaving the substance. For example enthalpy for water can be written H H20 (l) and for ice written H H20 (s).
To express the heat of a reaction at constant pressure (qp) a quantity called Enthalpy (H) is used.
H = E + (P.V)
DH = DE + (P. DV)
DH = (q + w) + (P. DV)
DH = qp - (P. DV) + (P. DV)
DH = qp
For chemical reactions:
DH = Hp - Hr
HP = enthalpy of product
Hr = reactant enthalpy
Reaction at constant pressure: qp = DH (enthalpy change)
Reaction at fixed volume: qv = DE (change in energy in)
Changes in heat or enthalpy that occur during the process of receiving or releasing heat are expressed as "change in enthalpy (ΔH)". The actual enthalpy of a substance cannot be determined or measured. But ΔH can be determined by measuring the amount of heat absorbed by the system. For example in the change of ice into water, which is 89 calories / gram.
At the change of ice into water, ΔH is positive, because the enthalpy of change results, the enthalpy of water is greater than the enthalpy of ice. In chemical changes there is always a change in enthalpy. The magnitude of the change in enthalpy is as large as the difference between the enthalpy of the reaction product and the amount of reactant enthalpy.
Every system or substance has energy stored in it. Potential energy is related to the form of matter, volume, and pressure. Kinetic energy is generated because atoms and molecules in substances move randomly. The total amount of all forms of energy is called enthalpy (H). Enthalpy will remain constant as long as there is no energy entering or leaving the substance. . For example enthalpy for water can be written H H20 (l) and for ice written H H20 (s).