9.1 Practice Problems

Attempt these problems as if they were real exam questions in an exam environment.

Only look up information if you get severely stuck. Never look at the solution until you have exhausted all efforts to solve the problem. Having to look up information or the solution should be an indicator that the previous layers (1–5) in the Structured Learning Approach have not been mastered.

  1. A flask containing two reactants produces enough heat to raise the temperature of 1.25 L of solution from 45 °C to 99 °C. What is the heat of the reaction (in kJ) assuming the density of the solution is exactly 1 g mL–1 and the specific heat of the solution is 4.184 J g–1 °C–1?

    1. 282
    2. 0.625
    3. –0.282
    4. –282
    5. –0.548

    Solution


  2. What is the change in internal energy (in J) of a system that does 2468.2 J of work on its surroundings and absorbs 25.2 J of heat?

    1. –2443
    2. 2443.0
    3. –2400.0
    4. 2400.0
    5. 2.493

    Solution


  3. The value of ΔH° for the reaction below is –6,535 kJ mol–1. What change in heat (in kJ) does the combustion reaction of 16.0 g of C6H6(l) experience?
    \[2\mathrm{C_6H_6}(l) + \mathrm{15O_2}(g) \longrightarrow \mathrm{12CO_2}(g) + \mathrm{6H_2O}(l)\]

    1. –1.34×103
    2. 5.23×104
    3. –669
    4. 2.68×103
    5. –6535

    Solution


  4. The specific heat of liquid bromine is 0.226 J g–1 °C–1. How much heat (in J) is required to raise the temperature of 10.0 mL of bromine from 25.00 °C to 27.30 °C? The density of liquid bromine is 3.12 g mL–1.

    1. 5.20
    2. 16.2
    3. 300
    4. 32.4
    5. 10.4

    Solution


  5. Given the following three reactions
    \[\begin{align*} \mathrm{N_2}(g) + \mathrm{O_2}(g) &\longrightarrow \mathrm{2NO}(g) \quad &&\Delta H = -180.5~\mathrm{kJ} \\ \mathrm{N_2}(g) + \mathrm{3H_2}(g) &\longrightarrow \mathrm{2NH_3}(g) \quad &&\Delta H = -91.8~\mathrm{kJ} \\ \mathrm{2H_2}(g) + \mathrm{O_2}(g) &\longrightarrow \mathrm{2H_2O}(g) \quad &&\Delta H = -483.6~\mathrm{kJ} \end{align*}\] calculate the enthalpy of reaction (in kJ) for the following reaction:
    \[4\mathrm{NH_3}(g) + \mathrm{5O_2}(g) \longrightarrow \mathrm{4NO}(g) + \mathrm{6H_2O}(g)\]

    1. –1628
    2. 1628
    3. –1995
    4. 1995
    5. –660

    Solution


  6. You are hoping to use specific heat to determine the identity of a metal. You weigh the piece of metal and find that it is 0.015 kg. You find that it requires 60.3 J to raise the temperature of this piece of metal by 10 °C. Of the options in the table, which is the most likely identity of the piece of metal?

    Metal Specific Heat (J g–1 °C–1)

    Gold  

    0.125604

    Copper  

    0.376812

    Iron  

    0.460548

    Brass (Yellow)  

    0.4019328

    Indium  

    0.2386476
    1. Brass
    2. Gold
    3. Copper
    4. Iron
    5. Indium

    Solution


  7. Which of the following statements best describes a state function?

    1. The final and initial states are the only ones that matter.
    2. The path, or the steps taken to get from point A to point B, matter.
    3. Only the initial state is taken into consideration.
    4. Only the final state is taken into consideration.
    5. The magnitude, but not the sign, of the values matters.

    Solution


  8. Using the data given, calculate the standard reaction enthalpy (in kJ mol–1) for a precipitation reaction when Pb(NO3)2 and NaCl solutions are mixed.

    Compound ΔHf° (kJ mol–1)

    Pb(NO3)2

    -454.9

    NaCl

    -411.2

    PbCl2

    -359.4

    NaNO3

    -467
    1. –16.1 kJ mol–1
    2. 16.1 kJ mol–1
    3. 39.7 kJ mol–1
    4. –39.7 kJ mol–1
    5. Not enough information given

    Solution


  9. A combustion reaction is conducted in a bomb calorimeter with a heat capacity of 1522 J °C–1. If the calorimeter temperature rises from 20.00 °C to 21.23 °C, how much thermal energy (in J) is released from the combustion reaction?

    1. 1,872
    2. 1,906
    3. 2,211
    4. 30,440
    5. 32,310

    Solution


  10. Identify the true statement about the following reaction:
    \[\mathrm{H_2} + \mathrm{O_2} \longrightarrow \mathrm{2H_2O} \quad \Delta H = -286~\mathrm{kJ~mol^{-1}}\]

    1. This reaction is an endothermic reaction.
    2. This reaction is an exothermic reaction.
    3. This reaction is not balanced.
    4. This reaction requires 2 moles of O2 to make 2 moles of H2O.
    5. There is no true statement.

    Solution


  11. A 60.5 g piece of copper (cCu = 0.377 J g–1 °C–1) was heated to 85.6 °C and submerged in 22.4 °C water of unknown mass. The metal and water reached an equilibrated temperature of 29.9 °C. Find the mass (in g) of the water if cwater = 4.184 J g–1 °C–1.

    1. 40.5
    2. 60.5
    3. 33.6
    4. 15.2
    5. 0.56

    Solution


  12. Use the given bond energies (in kJ mol–1) to calculate the approximate enthalpy change (ΔH in kJ) for the given reaction.
           CO(g) + 2H2(g) → CH3OH(g)
    C≡O: 1080
    H–H: 436
    C–H: 415
    C–O: 350
    O–H: 464

    1. 107
    2. 723
    3. –243
    4. 243
    5. –107

    Solution


  13. Which ionic compound in each of the following pairs is expected to have a lower melting temperature (i.e. lower lattice energy)?
         i. NaF and CsBr
         ii. MgO and RbS
         iii. CaS and Al2O3
         iv. CaO and CaS

    1. i: NaF    ii: MgO    iii: Al2O3    iv: CaO
    2. i: CsBr    ii: MgO    iii: Al2O3    iv: CaS
    3. i: CsBr    ii: MgO    iii: Al2O3    iv: CaO
    4. i: NaF    ii: MgO    iii: CaS    iv: CaS
    5. i: CsBr    ii: RbS    iii: CaS    iv: CaS

    Solution




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