Whether you want to be able to calculate the changes in enthalpy of a reaction, understand the difference between an exothermic or endothermic reaction, or know what enthalpy is, it might be a good idea for you to read on. This fantastic calculator can take care of all the hard work while educating you on processes that can be confusing without expert help.

What is Enthalpy?

Enthalpy is the process of measuring the energy of a thermodynamic system. The process takes place by multiplying the heat or volume by the pressure. It’s also a state function that depends on a system’s equilibrium state. 

The enthalpy can also refer to changes and the exchange of energy within a system. In essence, enthalpy is an energy transfer.

Reactions: Endothermic and Exothermic

The two primary types of thermodynamic reactions are endothermic and exothermic. Endothermic reactions are the result of absorbing heat from the surroundings, while exothermic reactions release heat into the surroundings. 

The similarity between the two is that both of them alter the energy level of their environment, causing differences in enthalpy. If the reaction is endothermic, the enthalpy change will be positive, and if the reaction is exothermic, the change in enthalpy will be negative. Negative means that heat is lost and released into your surroundings, while positive means it absorbs heat from the surroundings.

The Enthalpy Formula

Enthalpy is the sum of a system’s heat absorption and what occurs when it’s expanding. The formula looks like this: 

H = Q + PV

Q = internal energy
P = pressure
V = Volume

However, if you are calculating a change in enthalpy, you need to consider both its beginning and end state, taking into consideration that while the reaction is occurring, the pressure is constant. The formula, considering that, would be: 

ΔH = (Q₂ - Q₁) + p x (V₂ - V₁) or ΔH = ΔQ + p x ΔV

Q₂ and V₂ = internal energy and volume reaction/reactants 
P = constant pressure 
ΔQ = internal energy change
ΔV = volume change 
ΔH = enthalpy change

The Enthalpy of a Reaction and How to Calculate It

This enthalpy calculator allows you to calculate enthalpy with relative ease. You can also follow these steps below. 

   1.	Identify your volume change. For the sake of this example, we will assume it’s a three-liter change. 
   2.	Identify your internal energy change, which we can put at 1500 J. 
   3.	Measure the pressure of the surroundings. An example would be 2 atmosphere. 
   4.	Put all your identified values into the equation to find out what the change in enthalpy could be. 
ΔH = ΔQ + p x ΔV
ΔH = 1,500 J + 2 atm x 3 l = 1,500.6 J

If you want to find the enthalpy using the final energy and volume, you can also use the enthalpy calculator in advanced mode.