Thermochemistry IB Questions

Thermochemistry IB questions

1. Ammonium nitrate, NH4NO3, dissolves readily in water according to the equation:

NH4NO3(s)  NH4+(aq) + NO3-(aq) H = 28kJ mol-1

Which of the following contribute(s) to the occurrence of this process?

I. The system moves to lower enthalpy.
II. The system becomes more disordered.

a. I only
b. II only
c. Both I and II
d. Neither I nor II

2. Which substance has the largest lattice energy?

a. NaF b. KCl c. MgO d. CaS

3. A certain reaction is spontaneous below 100oC but is non-spontaneous at higher temperatures. Based on this information, what are the signs of H and S?

H S
a. - -
b. - +
c. + +
d. + -

4. Which ionisation requires the most energy?

a. Na(g)  Na+(g) + e-
b. Na+(g)  Na2+(g) + e-
c. Mg(g)  Mg+(g) + e-
d. Mg+(g)  Mg2+(g) + e-

5. The bond enthalpies in kJ mol-1 for several bonds are given below:

H – H 436 O – O 196 O = O 496 H – O 463

What is the enthalpy change, H, in kJ for the reaction below?

2 H2(g) + O2(g)  2 H2O(g)

a. 442
b. 92
c. - 484
d. - 834

6. At 0oC, the mixture formed when the following reaction reaches equilibrium consists mostly of N2O4(g)

2 NO2(g)  N2O4(g)

What are the signs G, H, S at this temperature?

G H S
a. + + +
b. - - -
c. - + +
d. + + -

7. Excess thionyl chloride, SOCl2, can be removed from a reaction mixture by reacting it with water according to the equation:

SOCl2(l) + H2O(l)  2 HCl(g) + SO2(g)

Use the following data to calculate the Ho for this reaction.

SOCl2(l) H2O(l) HCl(g) SO2(g) Hof (kJ mol-1) -245.6 -285.8 -92.3 -296.8

a. –142.3
b. –50.0
c. +50.0
d. +142.3

8. 200 J of energy were given to a 10 g sample of copper. If the temperature of the copper is increased by 50oC, what is the specific heat capacity of the copper?

a. 0.25 J g-1 oC-1
b. 0.40 J g-1 oC-1
c. 2.5 J g-1 oC-1
d. 4.0 J g-1 oC-1

9. Which of the changes below occurs with the