CalorimetryExperiment

CalorimetryExperiment - Calorimetry Experiment Enthalpy of...

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Calorimetry Experiment Enthalpy of Acid-Base Neutralization Reaction I Objective: Determine the molar enthalpies of reactions when a set of strong and weak acids react with a set of strong and weak bases using a Constant Pressure Calorimeter . II Discussions II.A Enthalpy Enthalpy (from the Greek word enthalpein , meaning "to warm") is defined as the heat absorbed or released under constant pressure. Enthalpy is denoted with the symbol H . We cannot measure the enthalpy of a system, but can measure the change in the change in enthalpy, which we represent by the symbol Δ H. II.B Sign Convention for Δ H: (a) If the system absorbs heat, Δ H will be positive ( Δ H > 0) and the process is called endothermic. (b) If the system loses heat, Δ H will be negative ( Δ H < 0) and the process is called exothermic. II.C Calorimetry The value of Δ H can be determined experimentally by measuring the heat flow accompanying a reaction at constant pressure. The measurement of heat flow is calorimetry ; an apparatus that measures heat flow is a calorimeter . Specific Heat of a substance The heat required to raise the temperature of 1 g of a substance by 1 K (or 1°C) is called its specific heat capacity , or merely its specific heat. The specific heat of a substance can be determined experimentally by measuring the temperature change, T , that a known mass, m , of the substance undergoes when it gains or loses a specific quantity of heat, q : () ( ) quantity of heat transferred Specific heat = grams of substance temperature change × = q m ×ΔΤ The heat capacity of 1 mol of a substance is called its molar heat capacity . quantity of heat transferred Molar Specific heat = mole of substance temperature change quantity of heat transferred = 1 mole of substance grams of substance temperature change molar mass of substance × ×
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The quantity of heat that a substance has gained or lost may be calculated from its specific heat together with its measured mass and temperature change. () ( ) mass of substance, g specific heat q mC =⋅⋅ Δ Τ × Δ Τ Constant-Pressure Calorimetry Although the calorimeters used for highly accurate work are precision instruments, a very simple "coffee-cup" calorimeter is often used in general chemistry labs to illustrate the principles of calorimetry. The heat gained by the solution, q soln , is readily calculated from the mass of the solution, its specific heat, and the temperature change: ( ) soln mass of solution, g specific heat of solution q × Δ Τ For dilute aqueous solutions, the specific heat of the solution will be approximately the same as that of water, 4.18 J/g-K. Coffee-cup calorimeter, in which reactions occur at constant pressure. The heat of the reaction, q rxn , is equal in magnitude and opposite in sign from q soln : ( )( ) soln fi mass of solution specific heat of solution rxn qq =− × × Τ −Τ
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III PREPARATORY QUESTIONS 1. The principal reaction which occurs between solutions of a strong acid and a strong base is identical regardless of the actual acid or base used. Write this net thermo-chemical equation including the
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This note was uploaded on 12/12/2011 for the course CHM 2041 taught by Professor Staff during the Fall '09 term at Santa Fe College.

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CalorimetryExperiment - Calorimetry Experiment Enthalpy of...

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