a. Define the terms exothermic and endothermic. In a calorimetric experiment, ho

Question

a. Define the terms exothermic and endothermic. In a calorimetric experiment, how does one determine whether a reaction is one or the other? b. In a calorimetric experiment, why is it important to determine the heat capacity of the calorimeter? Two solutions namely, 500 mL of 0.50 M HCl and 500 mL of 0.50 M NaOH at the same temperature of 24.5 degree C are mixed in a constant-pressure calorimeter. The heat capacity of the calorimeter was 550 J/degree C. Given that the specific heat of the solution is 4.184 J/g degree C, the density of the solution is 1.00 g/mL, and that the heat of neutralization for the process H^+ (aq) + OH^- (aq) rightarrow H_2O (1) is -56.2 kJ, what is the final temperature of the mixed solution?

Explanation / Answer

Q1.

a. exothermic --> a reaction/process that will RELEASE energy in the form of HEAT

endothermic --> a reaction/process that will ABSORB energy in the form of HEAT

we typically state in calorimetry:

drop of temperature in the calorimeter --> Caloimeter is the surroundings, so it is losing heat, so the reaction is absorbing it, i.e. the reaciton is endothermic....

Same for exothermic --> expect an increase in temperature in the surroundings

b)

We need heat capacity because the system is NOT IDEAL, that is, the calorimeter is absorbing heat... We need to account for it.

Q2.

Vtotal = 500+500 = 1000 mL = 1000 g

mol of acid = MV = 0.5*0.5 = 0.25 mol of acid/base

Qcalorimter = Qrxn

Qfrom reaction = n*HRxn = (0.25)(56.2) = -14.05 kJ = -14500 J

Q absorbed = Qsolution + Qcalorimeter

Qsolution = m*Cp*(Tf-Ti)

Qcalorimeter = C*(Tf-Ti)

14500 = m*Cp*(Tf-Ti) + C*(Tf-Ti)

14500 = 1000*4.184*(Tf-24.5) + 550(Tf-24.5)

14500 =4184*(Tf-24.5) + 550(Tf-24.5)

14500 = (4184+550)Tf + (4184)(-24.5) + (550)(-24.5)

4734Tf = 14500 - ( (4184)(-24.5) + (550)(-24.5)) = 130483

Tf = (130483)/4734

Tf = 27.562°C final

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