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How do you calculate the energy change of a reaction?

The energy change of a reaction is calculated by subtracting the energy of the reactants from the energy of the products.

In a chemical reaction, energy is either absorbed or released. This energy change is often referred to as the enthalpy change and is represented by the symbol ΔH. The energy change of a reaction can be calculated using the formula ΔH = H(products) - H(reactants), where H represents the total energy of the molecules.

To calculate the energy change, you first need to know the energy of the reactants and the energy of the products. These values are usually given in kilojoules per mole (kJ/mol) and can be found in tables of standard enthalpies of formation. The energy of the reactants is the energy required to break the bonds in the reactants, and the energy of the products is the energy released when the new bonds in the products are formed.

Subtract the total energy of the reactants from the total energy of the products to find the energy change. If the result is negative, the reaction is exothermic, meaning it releases energy. If the result is positive, the reaction is endothermic, meaning it absorbs energy.

For example, if the energy of the reactants is 500 kJ/mol and the energy of the products is 300 kJ/mol, the energy change would be 300 kJ/mol - 500 kJ/mol = -200 kJ/mol. This means the reaction is exothermic and releases 200 kJ of energy per mole of reactant.

Remember, energy changes in reactions are important because they tell us whether a reaction will occur spontaneously. Reactions that release energy (exothermic reactions) are more likely to occur than those that absorb energy (endothermic reactions).

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