A sample of a hydrocarbon is combusted completely in O21g2 to produce 21.83 g CO21g2, 4.47 g H2O1g2, and 311 kJ of heat. (a) What is the mass of the hydrocarbon sample that was combusted?

검증된 단계별 안내

Identify the chemical reaction involved: The complete combustion of a hydrocarbon (CxHy) in oxygen (O2) produces carbon dioxide (CO2) and water (H2O).

Use the given masses of CO2 and H2O to determine the moles of each product formed. Use the molar mass of CO2 (44.01 g/mol) and H2O (18.02 g/mol) for these calculations.

Determine the moles of carbon and hydrogen in the hydrocarbon by using the stoichiometry of the combustion reaction. Each mole of CO2 corresponds to one mole of carbon, and each mole of H2O corresponds to two moles of hydrogen.

Calculate the mass of carbon and hydrogen in the hydrocarbon sample using their respective atomic masses (C: 12.01 g/mol, H: 1.008 g/mol).

Add the masses of carbon and hydrogen to find the total mass of the hydrocarbon sample that was combusted.

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주요 개념

질문에 올바르게 답하기 위해 반드시 이해해야 하는 핵심 개념들은 다음과 같습니다.

Combustion Reaction

A combustion reaction is a chemical process in which a substance (usually a hydrocarbon) reacts with oxygen to produce carbon dioxide and water, releasing energy in the form of heat. In this case, the complete combustion of the hydrocarbon generates specific amounts of CO2 and H2O, which can be used to determine the mass of the original hydrocarbon.

Stoichiometry

Stoichiometry is the calculation of reactants and products in chemical reactions based on the conservation of mass. It involves using molar ratios derived from balanced chemical equations to relate the amounts of substances consumed and produced. In this question, stoichiometry will help relate the masses of CO2 and H2O produced to the mass of the hydrocarbon that was combusted.

Molar Mass

Molar mass is the mass of one mole of a substance, typically expressed in grams per mole (g/mol). It is essential for converting between the mass of a substance and the number of moles, which is crucial in stoichiometric calculations. To find the mass of the hydrocarbon, the molar masses of CO2 and H2O will be used to determine the moles produced, which can then be related back to the original hydrocarbon sample.

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교과서 질문

Consider two solutions, the first being 50.0 mL of 1.00 M CuSO₄ and the second 50.0 mL of 2.00 M KOH. When the two solutions are mixed in a constant-pressure calorimeter, a precipitate forms and the temperature of the mixture rises from 21.5 to 27.7 °C (d) From the calorimetric data, calculate ΔH for the reaction that occurs on mixing. Assume that the calorimeter absorbs only a negligible quantity of heat, that the total volume of the solution is 100.0 mL, and that the specific heat and density of the solution after mixing are the same as those of pure water.

One of the best-selling light, or low-calorie, beers is 4.2% alcohol by volume and a 355-mL serving contains 110 Calories; remember: 1 Calorie = 1000 cal = 1 kcal. To estimate the percentage of Calories that comes from the alcohol, consider the following questions. (a) Write a balanced chemical equation for the reaction of ethanol, C2H5OH, with oxygen to make carbon dioxide and water. (b) Use enthalpies of formation in Appendix C to determine ΔH for this reaction. (c) If 4.2% of the total volume is ethanol and the density of ethanol is 0.789 g/mL, what mass of ethanol does a 355-mL serving of light beer contain? (d) How many Calories are released by the metabolism of ethanol, the reaction from part (a)? (e) What percentage of the 110 Calories comes from the ethanol?

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교과서 질문

The methane molecule, CH4, has the geometry shown in Figure 2.17. Imagine a hypothetical process in which the methane molecule is 'expanded,' by simultaneously extending all four C—H bonds to infinity. We then have the process CH41g2¡C1g2 + 4 H1g2 (a) Compare this process with the reverse of the reaction that represents the standard enthalpy of formation of CH41g2.

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