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# Enthalpy Calculator

Enter the values to calculate the enthalpy change using the formula or chemical reaction scheme.

ΔH = ΔQ + p * ΔV

## Enthalpy Calculator

This enthalpy calculator calculates the enthalpy change (ΔH) involved in a process along with the initial and final enthalpy values using Hess's Law or standard enthalpies of formation. It provides valuable insights into chemical reactions to help you analyze energy variations and understand the thermodynamics of the system.

## What Is Enthalpy?

Enthalpy measures the total energy released or absorbed in a thermodynamic system. It is the sum of the total internal energy and the product of pressure and volume.

Whenever a system changes its state from solid to liquid or liquid to gas, it requires sufficient energy intake. It is called the latent heat of fusion or vaporization, respectively. The latent heat of fusion and vaporization are specific examples of enthalpy changes associated with phase transitions.

Enthalpy = H = U + PV

Where:

• H = Enthalpy
• E = Internal energy
• V = Volume
• P = Pressure

According to System International (SI), the enthalpy is expressed in joules (J) or kilojoules (kJ). As it's not possible to directly calculate the total enthalpy of a chemical reaction, the change in enthalpy is calculated. This change indicates the amount of heat absorbed or released during the reaction. There are two types of reactions:

• Exothermic: In these reactions, the heat is released to the surroundings and the value of enthalpy change (ΔH) is negative
• Endothermic: These reactions absorb heat and the enthalpy change (ΔH) is positive

### Enthalpy Change Equation:

ΔH = ΔQ + p * ΔV

Where:

• ΔH is the change in heat of a system
• ΔQ is the change in the internal energy of a system
• P is pressure on the system due to the surroundings
• ΔV is the change in the volume of the system

#### For a General Reaction:

anA + bnB + cnC → dnD + enE + fnF

The formula for standard enthalpy of formation is given below:

“ΔH° of reaction = ∑ΔH°f(products) - ∑ΔH°f(reactants)”

Where:

• A, B, and C are reactants
• an, bn, and cn are the coefficients of the reactants
• dn, and fn are coefficients of products formed
• D, E, and F are products
• ∑ΔH°f(products) indicates the change in heat during the formation of the product
• ∑ΔH°f(reactants) is the change in heat of reactants

## Example (Enthalpy Change):

Suppose a chemical reaction occurs at a constant pressure of 45 Pascals. The reactants possess an internal energy of 55 Joules and obtain a volume of 65 cubic meters. Now system transitions to a state where the products exhibit an internal energy of 45 Joules and occupy a volume of 35 cubic meters. Calculate the initial, final enthalpies, and the enthalpy change.

Solution:

Given that:

• Internal Energy of Reactants = 55 J
• Internal Energy of Products = 45 j
• Volume of Reactants = 65 cu m3
• Volume of Products = 35 cu m3
• Constant Pressure = 45 Pa

Let's find Δ U:

Δ U = U(products) - U_(reactants) = 45 j - 55 j = -10 j

Now calculate ΔV:

Δ V = V(products) - Vreactants = 35 m3 - 65 m3 = - 30 m3

Find P ΔV:

P ΔV = 45 Pa x (-30 m3) = -1350 j

Finally, find delta h:

Δ H = Δ U + P ΔV = -10 j + (-1350 j) = -1360 J

The change in enthalpy of reaction is:

Δ H = -1360 j

Initial enthalpy (H(initial)):

For the reactants:

H(initial) = Ureactants + P Vreactants = 55 j + 45 Pa x 65 m3

Calculate the term (P V(reactants)):

P V(reactants = 45 Pa x 65 m3 = 2925 j

So,

H(initial) = 55 j + 2925 j = 2980 j

Final enthalpy (H(final)):

For the products:

H(final) = U(products) + P V(products) = 45 j + 45 Pa x 35 m3

Calculate the term PVproducts):

PVproducts) = 45 Pa x 35 m3 = 1575 j

So, the final enthalpy is:

H(final) = 45 j + 1575 j = 1620 j

After performing the calculation we get - 1360 j as enthalpy change. This negative sign indicates that it's an exothermic reaction. The calculations become even easier with the use of an online enthalpy calculator because it provides you with the step-by-step calculation of enthalpy change.

## The Enthalpy Table:

 Sr No. Name of Substance Symbolic Formula Standard Enthalpy of Formation ‘ΔH’ 1. Potassium Chloride KCl(s) -435.9 2. Potassium Chlorate KClO3(s) -391.4 3. Sodium Chloride NaCl(s) -411.0 4. Sodium Hydroxide NaOH(s) -426.7 5. Zinc Sulphide ZnS(s) -202.9 6. Zinc Oxide ZnO(s) -348.0 7. Copper Sulphate CuSO4(s) -769.9 8. Copper Oxide CuO(s) -155.2 9. Calcium Dioxide Ca(OH)2(s) -986.6 10. Water H2O(l) -285.8 11. Chloroform CHCl3(l) -131.8 12. Carbon Dioxide CO2(g) -393.5 13. Hydrogen Sulphide H2S(g) -20.1 14. Ammonia NH3(g) -46.2 15. Sulphur Trioxide So3(g) -395.2 16. Hydrochloric Acid HCl(g) -92.3 17. Nitrogen Oxide NO(g) +90.4 18. Nitrogen Dioxide NO2(g) +33.9 19. Phosphorus Pentachloride PCl5(g) -398.9 20. Phosphorus Trichloride PCl3(g) -306.4 21. Sulphur Dioxide SO2(g) -296.1

## FAQ’s:

### What Are The Three Ways For Calculating Enthalpy Change?

• Hess’s Law
• Standard Enthalpies of Formation (ΔHf°)
• Bond Enthalpies

### What Is The Hess Law of Enthalpy?

The Hess law states, "No matter whether the reaction happens in one step or multiple steps, the energy released or absorbed during the chemical reaction is the same”.

### Why is Calculating Enthalpy Important?

Determining the enthalpy is important for various reasons including:

• Understanding energy changes
• Predicting whether a reaction is endothermic or exothermic
• Optimize the usage of energy
• Designing and optimizing the industrial processes
• Assessing the environmental impact of various processes

### Is Enthalpy Higher In Solid or Liquid?

Liquids have higher enthalpy as compared to the solids because of:

• Increased particle movement
• Weaker intermolecular forces

### Can I Calculate Enthalpy For A Mixture of Substances?

Yes, it can be calculated but it's complex because the interaction of substances with different components can affect the enthalpy

References:

From the source of Wikipedia: Enthalpy