# Enthalpy Calculator

H= m x SH x ΔT

Enthalpy= mass x Specific heat of substance x change in temperature

This enthalpy calculator calculates the enthalpy of a substance.

Enthalpy is the measure of the heat content of a substance. It is how much heat the substance contains.

Enthalpy is all the heat in a substance calculated from an accepted reference temperature. This reference temperature changes depending on the enthalpy of the substance being observed. For water, the enthalpy is usually measured from a reference temperature of 32°F. In case you forgot, 32°F represents the freezing point of water. Any temperature above this value is above freezing and therefore extends into a heating range (since above freezing). Since all temperatures above this point is above freezing, in this way, in a way, it represents a heating. For refrigerants, the reference temperature is usually -40°F. For air, the reference temperature is normally 77°F.

Enthalpy is affected by 3 factors or variables. The 3 variables are the mass of the substance, m, the specific heat (capacity) of the substance, sp. ht, and the difference in temperature between the temperature the substance is exposed to and the reference temperature.

The mass of the substance is how much matter a substance contains. The larger the mass, the greater the enthalpy because the more matter there is inside of the substance to absorb heat. Therefore, the greater the mass, the greater the enthalpy. Conversely, the smaller the mass, the smaller the enthalpy.

The specific heat (capacity) of a substance is the amount of heat necessary to raise the temperature of 1lb of the substance 1°F. Every substance has a different specific heat. For example, the specific heat of water is 1Btu/lb/°F. This means that 1 lb of water will be raised 1°F if 1 Btu is applied to it. The specific heat of copper is 0.092. This means that copper has a lower specific heat than water. Therefore, less heat is required to raise its temperature. So in rule, the greater the specific heat of a substance, the more thermal energy it takes to heat the object up. The smaller the specific heat, the less thermal energy it takes to heat the object up. The specific heat of a substance is measured in Btu/lb•°F.

The change in temperature, ΔT, is the difference in temperature between the temperature the substance is exposed to and the reference temperature. So if a substance is exposed to 100°F and the reference temperature is 32°F, the change in temperature will be 100°F - 32°F= 68°F. The greater the change in temperature, the greater the enthalpy, since the substance is exposed to a greater temperature. The smaller the ΔT, the smaller the enthalpy, since object is exposed to a lower temperature. The ΔT is measured in °F.

To use this calculator, a user must enter the mass of the substance, m, the specific heat of the substance, and the change in temperature, ΔT, and click the 'Calculate' button. The resultant enthalpy value will then be automatically calculated and shown.

The enthalpy value is measured in unit Btu but its most common unit is joules.

**Example Calculation**

What is the enthalpy of a 1lb of water at 212°F, assuming the reference tempreature is 32°F?

So based on the values of the parameters, we use the equation **H= m x sp. ht. x ΔT** and substitute in the values into the equation.

**H= (1lb)(1Btu/lb•°F)(212°F - 32°F)= 180 Btu or Joules**

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