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Experimental Application of Hess Law

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Introduction The energy content of a substance, called its enthalpy, cannot be measured. However, the enthalpy change, ∆H, of a chemical reaction can be measured. Most chemical reactions are accompanied by energy changes, usually in the form of heat energy. The enthalpy change of a reaction is the heat energy released or absorbed in a chemical reaction. Exothermic reactions are reactions that releases heat energy to the surroundings. The enthalpy of the products is lower than that of the reactants. So, ∆H is negative and its temperature of the mixture increases. Some examples of exothermic reactions have dissolution of sodium hydroxide in water, dilution of a conc. Acid, neutralization and bond formation. For calculate the amount of heat released from the reaction in this experiment, the equation can be expressed as qreaction = qsolution+ qcalorimeter − ①
In this experiment, the calorimeter is absorb a very little heat or can be said that nearly to zero. Therefore the qcalorimeter can be neglect in the equation ① as well. This is because the small value of it have. Thus, the equation can be simplifies to qreaction = qsolution − ②
Next, the temperature change caused by the addition of a given amount of heat will depend on the specific heat capacity, Csp of the substances. Thus, the heat involved in this experiment can be calculated from this following equation.
Q = (Csp)(m)(∆T) − ③ where, m is the mass of substances, ∆T is the temperature change which is the differences between the final temperature and the initial temperature. Based on the first law of thermodynamics, the heat energy supplied to a gas equals the sum of the increase in internal energy of the gas and the work done by the gas, which can be expressed in this equation form Q = ∆U + W where ∆Q = heat energy supplied, ∆U = increase in

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