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Ch.5 - Thermochemistry
All textbooksBrown 14th EditionCh.5 - ThermochemistryProblem 109
Chapter 5, Problem 109

Burning acetylene in oxygen can produce three different carbon-containing products: soot (very fine particles of graphite), CO(g), and CO2(g). (a) Write three balanced equations for the reaction of acetylene gas with oxygen to produce these three products. In each case assume that H2O(l) is the only other product. Determine the standard enthalpies for the reactions in part (a).

Verified step by step guidance
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Step 1: Write the balanced chemical equation for the complete combustion of acetylene (C2H2) to produce carbon dioxide (CO2) and water (H2O). The general form is: C2H2 + O2 -> CO2 + H2O. Balance the equation by ensuring the number of atoms of each element is equal on both sides.
Step 2: Write the balanced chemical equation for the incomplete combustion of acetylene to produce carbon monoxide (CO) and water (H2O). The general form is: C2H2 + O2 -> CO + H2O. Balance the equation by adjusting the coefficients to ensure the conservation of mass.
Step 3: Write the balanced chemical equation for the combustion of acetylene to produce soot (graphite, C) and water (H2O). The general form is: C2H2 + O2 -> C + H2O. Balance the equation by ensuring the number of carbon, hydrogen, and oxygen atoms are equal on both sides.
Step 4: Determine the standard enthalpy change (ΔH°) for each reaction. Use standard enthalpy of formation values from a data table for each reactant and product. Apply Hess's Law: ΔH° = ΣΔH°f(products) - ΣΔH°f(reactants).
Step 5: Calculate the standard enthalpy change for each reaction using the balanced equations and the standard enthalpy of formation values. This involves substituting the values into the equation from Step 4 and performing the arithmetic to find ΔH° for each reaction.
Related Practice
Textbook Question

A coffee-cup calorimeter of the type shown in Figure 5.18 contains 150.0 g of water at 25.1°C A 121.0-g block of copper metal is heated to 100.4°C by putting it in a beaker of boiling water. The specific heat of Cu(s) is 0.385 J/g-K The Cu is added to the calorimeter, and after a time the contents of the cup reach a constant temperature of 30.1°C (d) What would be the final temperature of the system if all the heat lost by the copper block were absorbed by the water in the calorimeter?

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Textbook Question

(b) Assuming that there is an uncertainty of 0.002 °C in each temperature reading and that the masses of samples are measured to 0.001 g, what is the estimated uncertainty in the value calculated for the heat of combustion per mole of caffeine?

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Open Question
The corrosion (rusting) of iron in oxygen-free water includes the formation of iron(II) hydroxide from iron by the following reaction: Fe(s) + 2 H2O(l) → Fe(OH)2(s) + H2(g). (b) Calculate the number of grams of Fe needed to release enough energy to increase the temperature of 250 mL of water from 22 to 30 °C.
Textbook Question

We can use Hess's law to calculate enthalpy changes that cannot be measured. One such reaction is the conversion of methane to ethane: 2 CH4(g) → C2H6(g) + H2(g) Calculate the ΔH° for this reaction using the following thermochemical data: CH4(g) + 2 O2(g) → CO2(g) + 2 H2O(l) ΔH° = -890.3 kJ 2 H2(g) + O2(g) → 2 H2O(l) H° = -571.6 kJ 2 C2H6(g) + 7 O2(g) → 4 CO2(g) + 6 H2O(l) ΔH° = -3120.8 kJ

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Textbook Question

From the following data for three prospective fuels, calculate which could provide the most energy per unit mass and per unit volume:

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Open Question
The hydrocarbons cyclohexane (C6H12), ΔHf° = -156 kJ/mol, and 1-hexene (C6H12), ΔHf° = -74 kJ/mol, have the same empirical formula. (a) Calculate the standard enthalpy change for the transformation of cyclohexane to 1-hexene. (b) Which has greater enthalpy, cyclohexane or 1-hexene?