A calorimeter is an insulated device in which a chemical reaction is contained.
ID: 494719 • Letter: A
Question
A calorimeter is an insulated device in which a chemical reaction is contained. By measuring the temperature change. Delta T, we can calculate the heat released or absorbed during the reaction using the following equation: q = specific heat times mass times Delta T Or, if the calorimeter has a predetermined heat capacity, C, the equation becomes q = C times Delta T At constant pressure, the enthalpy change for the reaction, Delta H, is equal to the heat, q_p; that is, Delta H = q_p but it is usually expressed per mole of reactant and with a sign opposite to that of q for the surroundings. The total internal energy change, Delta E (sometimes referred to as Delta U), is the sum of heat, q. and work done, omega: Delta E = q + omega However, at constant volume (as with a bomb calorimeter) omega = 0 and so Delta E = q_v. Part A A calorimeter contains 31.0 mL of water at 11.5 degree C. When 1.90 g of X (a substance with a molar mass of 60.0 g/mol) is added, it dissolves via the reaction X(s)+H_2O (l) rightarrow X(aq) and the temperature of the solution increases to 28.0 degree C. Calculate the enthalpy change, Delta H, for this reaction per mole of X. Assume that the specific heat of the resulting solution is equal to that of water [4.18 J./(g middot degree O)], that density of water is 1.00 g/mL, and that no heat is lost to the calorimeter itself, nor to the surroundings. Express the change in enthalpy in kilojoules per mole to three significant figures. Delta H = _______ kJ/molExplanation / Answer
Heat change of water, q1 = ms(t2-t1)
q1 = 31.0 * 4.184 * (28.0 - 11.5)
q1 = 2140.12 J
Since the system follows adiabatic condition, this amount of heat should supplied from the substance X while dissolveing in water.
Now, moles of X = 1.90 / 60.0 = 0.0317 mol
Therefore, delta H = q1 / n
= 2140.12 / 0.037
= 57841.1 J/mol
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