a) (5 points) Use the following bond energies to estimate the value of the stand

Question

a) (5 points) Use the following bond energies to estimate the value of the standard heat of formation (AH 5. of gas phase ammonia from its elements in their standard states. N2(9) +3H2(g) 2NH3(g) Bond energies (kJ/mol): N N 945, N-H 391, H-H 436 b) (10 points) 0.200L of 0.200M HCI is mixed with an equal volume of 0 .200M NaOH in a constant pressure calorimeter. A temperature rise from 22.15 C to 23.48°C is measured as a consequence of the reaction that occurs. Calculate AH for the reaction, assuming that the density of the mixture as well as it's specific heat are the same as that of pure water (1.00g/mL and 4.186J/g oC, respectively).

Explanation / Answer

Q5

a)

HRxn = Hprodcuts- Hreactants

-HRxn = Hformed- Hbroken

- Hrxn = (6x(N-H)) - (N(triple)N + 3H-H))

- Hrxn = 6 *391 - (945 + 436*3) = 93

HRxn = -93 kJ/mol

b)

HRxn = -Qsolution / n

n = MV = 0.2*0.2 = 0.04 mol

Qsoln = m*C*(Tf-Ti)

Vtotal = 0.2+0.2 = 0.4 L = 400 mL = 400 g

Qsoln = 400*4.186*(23.48-22.15) = 2226.952 J

HRxn = -2226.952 /0.04 = -55673.8 J/mol

HRxn = -55.674 kJ/mol

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