Chapter 8: Thermochemistry Problems

What is the enthalpy for the following reaction? overall: C + 12O2→CO

-110 kJ/mol

Determine the enthalpy for this reaction: Ca(OH)2(s)+CO2(g)→CaCO3(s)+H2O(l)

-113.2 kJ/mol

What is ΔH∘rxn for the following chemical reaction? CO2(g)+2KOH(s)→H2O(g)+K2CO3(s) You can use the following table of standard heats of formation (ΔH∘f) to calculate the enthalpy of the given reaction.

-149 kJ

Click on the Delta H changes sign whan a process is reversed button within the activity and analyze the relationship between the two reactions that are displayed. The reaction that was on the screen when you started and its derivative demonstrate that the reaction enthalpy, ΔH, changes sign when a process is reversed. Consider the reaction H2O(l)→H2O(g), ΔH =44.0kJ What will ΔH be for the reaction if it is reversed

-44.0 kJ

Consider the reaction Ca(OH)2(s)→CaO(s)+H2O(l) with enthalpy of reaction ΔHrxn∘=65.2kJ/mol What is the enthalpy of formation of CaO(s)?

-635.1 kJ/mol

Calculate the approximate enthalpy change , ΔH∘, for the combustion of methane: CH4+2O2⇌2H2O+CO2 Use the values you calculated in Parts A to D, keeping in mind the stoichiometric coefficients.

-668 kJ

Click on the Hess's law of constant heat summation button within the activity and use the example shown to calculate the reaction enthalpy, ΔH, for the following reaction: CH4(g)+2O2(g)→CO2(g)+2H2O(l)Use the series of reactions that follow: C(s)+2H2(g)→CH4(g), ΔH =−74.8 kJ. C(s)+O2(g)→CO2(g), ΔH =−393.5 kJ. 2H2(g)+O2(g)→2H2O(g), ΔH =−484.0 kJ. H2O(l)→H2O(g), ΔH =44.0 kJ.

-890.7 kJ

What is the specific heat of silver?

0.235 J⋅(g⋅∘C)^−1

The amount of boiling water required to raise the temperature of 25.0 kg of water in the bath to body temperature is 4.80 kg. In this process, the heat lost by the boiling water is equal to the heat gained by the room-temperature water. How much heat was transferred in this process?

1225 kJ

Calculate the bond dissociation energy needed to break all the bonds in a mole of carbon dioxide, CO2.

1464 kJ/mol

Calculate the bond dissociation energy for the breaking of all the bonds in a mole of methane, CH4.

1640 kJ/mol

An ideal gas (which is is a hypothetical gas that conforms to the laws governing gas behavior) confined to a container with a massless piston at the top. (Figure 2) A massless wire is attached to the piston. When an external pressure of 2.00 atm is applied to the wire, the gas compresses from 6.60 to 3.30 L . When the external pressure is increased to 2.50 atm, the gas further compresses from 3.30 to 2.64 L . In a separate experiment with the same initial conditions, a pressure of 2.50 atm was applied to the ideal gas, decreasing its volume from 6.60 to 2.64 L in one step. If the final temperature was the same for both processes, what is the difference between q for the two-step process and q for the one-step process in joules?

167 J

If ΔH = -50.0 kJ and ΔS = -0.300 kJ/K , the reaction is spontaneous below a certain temperature. Calculate that temperature.

167 K

In the following experiment, a coffee-cup calorimeter containing 100 mL of H2O is used. The initial temperature of the calorimeter is 23.0 ∘C. If 3.00 g of CaCl2 is added to the calorimeter, what will be the final temperature of the solution in the calorimeter? The heat of solution ΔHsoln of CaCl2 is −82.8 kJ/mol. Assume that the specific heat of the solution formed in the calorimeter is the same as that for pure water: Cs=4.184 J/g⋅∘C.

28.2 ∘C

What is the enthalpy for reaction 1 reversed? reaction 1 reversed: CO2→CO + 12O2

283 kJ/mol

For the reaction given in Part A, ΔS∘rxn is 25.0 J/K . What is the standard Gibbs free energy of the reaction, ΔG∘rxn?

298 kJ

Calculate the standard enthalpy change for the reaction 2A+B⇌2C+2D where the heats of formation are given in the following table:

305 kJ

How much boiling water would you need to raise the bath to body temperature (about 37 ∘C)? Assume that no heat is transferred to the surrounding environment.

4.8 kg

For the reaction given in Part A, how much heat is absorbed when 2.90 mol of A reacts?

442 kJ

What is the bond dissociation energy for breaking all the bonds in a mole of O2 molecules?

495 kJ/mol

Calculate the enthalpy change, ΔH, for the process in which 36.2 g of water is converted from liquid at 12.1 ∘C to vapor at 25.0 ∘C . For water, ΔHvap = 44.0 kJ/mol at 25.0 ∘C and Cs = 4.18 J/(g⋅∘C) for H2O(l).

90.4 kJ

How many grams of ice at -14.8 ∘C can be completely converted to liquid at 22.6 ∘C if the available heat for this process is 4.14×103 kJ ? For ice, use a specific heat of 2.01 J/(g⋅∘C) and ΔHfus=6.01kJ/mol .

9040 g

Calculate the bond dissociation energy required for breaking all the bonds in a mole of water molecules, H2O.

920 kJ/mol

It takes 50.0 J to raise the temperature of an 11.6 g piece of unknown metal from 13.0∘C to 25.0 ∘C. What is the specific heat for the metal?

Cs =0.359 J⋅(g⋅∘C)^−1

Calculate the enthalpy change for the thermite reaction: 2Al(s)+Fe2O3(s)→2Fe(s)+Al2O3(s), ΔH∘rxn=−850 kJ when 12.0 mol of Al undergoes the reaction with a stoichiometrically equivalent amount of Fe2O3.

Enthalpy change of reaction when 12.0mol of Al reacts= multiplication factor×ΔH∘rxn when two moles of Al react = 12.0mol2 mol×(−850 kJ) = −5100 kJ

Classify the following by the sign of ΔE for the system.

Negative: The system expands and the surroundings get hotter. Positive: The system contracts and the surroundings get colder. Not enough data: The system expands and the surroundings get colder. The system contracts and the surroundings get hotter.

The equations given in the problem introduction can be added together to give the following reaction: overall: C + 12O2→COC + 12O2→CO However, one of them must be reversed. Which one?

Reaction 1: CO + 12O2→CO2

What can be said about an exothermic reaction with a negative entropy change?

Spontaneous at low temperatures

Watch the video of the thermite reaction, and then choose which of the following statements are correct for the thermite reaction.

The internal energy of the reactants is more than the internal energy of the products. The enthalpy change for the system is negative. The internal energy of the system decreases.

The molar heat capacity of silver is 25.35 J/mol⋅∘C. How much energy would it take to raise the temperature of 11.6 g of silver by 12.2 ∘C?

q= 33.2 J

What can be said about an endothermic reaction with a negative entropy change?

spontaneous in the reverse direction at all temperatures.

A piston has an external pressure of 14.0 atm. How much work has been done in joules if the cylinder goes from a volume of 0.180 liters to

w = -425 J

An ideal gaseous reaction (which is a hypothetical gaseous reaction that conforms to the laws governing gas behavior) occurs at a constant pressure of 30.0 atm and releases 68.0 kJ of heat. Before the reaction, the volume of the system was 8.80 L . After the reaction, the volume of the system was 2.60 L . Calculate the total internal energy change, ΔE, in kilojoules.

ΔE = -49.2 kJ

Consider the reaction C12H22O11(s)+12O2(g)→12CO2(g)+11H2O(l) in which 10.0 g of sucrose, C12H22O11, was burned in a bomb calorimeter with a heat capacity of 7.50 kJ/∘C. The temperature increase inside the calorimeter was found to be 22.0 ∘C. Calculate the change in internal energy, ΔE, for this reaction per mole of sucrose.

ΔE = -5650 kJ/mol

A total of 2.00 mol of a compound is allowed to react with water in a foam coffee cup and the reaction produces 157 g of solution. The reaction caused the temperature of the solution to rise from 21.00 to 24.70 ∘C. What is the enthalpy of this reaction? Assume that no heat is lost to the surroundings or to the coffee cup itself and that the specific heat of the solution is the same as that of pure water.

ΔH = -1.22 kJ/mol

A calorimeter contains 23.0 mL of water at 11.0 ∘C . When 2.10 g of X (a substance with a molar mass of 57.0 g/mol ) is added, it dissolves via the reaction X(s)+H2O(l)→X(aq) and the temperature of the solution increases to 29.0 ∘C . Calculate the enthalpy change, ΔH, 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⋅∘C)], that density of water is 1.00 g/mL, and that no heat is lost to the calorimeter itself, nor to the surroundings.

ΔH = -51.3 kJ/mol

Click the DeltaH is an Extensive Property button within the activity, and analyze the relationship between the two reactions that are displayed. The reaction that was on the screen when you started and its derivative demonstrate that the change in enthalpy for a reaction, ΔH, is an extensive property. Using this property, calculate the change in enthalpy for Reaction 2. Reaction 1: C3H8(g)+5O2(g)→3CO2(g)+4H2O(g), ΔH1=−2043 kJ Reaction 2: 5C3H8(g)+25O2(g)→15CO2(g)+20H2O(g), ΔH2=?

ΔH2 = −1.022×10^4 kJ

Calculate the standard enthalpy of the reaction, ΔH∘rxn, for the thermite reaction: 2Al(s)+Fe2O3(s)→2Fe(s)+Al2O3(s) Elements in their standard state have an enthalpy of formation value of zero. The standard enthalpies of formation of Fe2O3 and Al2O3 are ΔH∘f of Fe2O3(s)=−825.5 kJ/molΔH∘f of Al2O3(s)=−1675 kJ/mol

ΔH∘rxn = ∑ products nΔH∘f−∑reactants mΔH∘f = (−1675 kJ)−(−825.5 kJ) = −850 kJ