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Ch.6 - Gases
Tro - Chemistry: A Molecular Approach 6th Edition
Tro6th EditionChemistry: A Molecular ApproachISBN: 9780137832217Not the one you use?Change textbook
All textbooksTro 6th EditionCh.6 - GasesProblem 80
Chapter 6, Problem 80

Consider the chemical reaction: 2 H2O(l) → 2 H2(g) + O2(g) What mass of H2O is required to form 1.85 L of O2 at a temperature of 315 K and a pressure of 0.981 atm?

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Use the ideal gas law to find the number of moles of O2. The ideal gas law is given by the equation: \( PV = nRT \), where \( P \) is the pressure, \( V \) is the volume, \( n \) is the number of moles, \( R \) is the ideal gas constant (0.0821 L·atm/mol·K), and \( T \) is the temperature in Kelvin.
Rearrange the ideal gas law to solve for \( n \): \( n = \frac{PV}{RT} \). Substitute the given values for \( P \), \( V \), and \( T \) into the equation to calculate the moles of O2.
Use the stoichiometry of the balanced chemical equation to find the moles of H2O required. According to the equation, 2 moles of H2O produce 1 mole of O2. Therefore, multiply the moles of O2 by 2 to find the moles of H2O needed.
Convert the moles of H2O to grams. Use the molar mass of H2O (approximately 18.02 g/mol) to convert moles to grams by multiplying the moles of H2O by the molar mass.
Summarize the steps and ensure all units are consistent throughout the calculations to find the mass of H2O required.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Stoichiometry

Stoichiometry is the calculation of reactants and products in chemical reactions based on the balanced equation. It allows us to determine the relationships between the amounts of substances involved. In this case, the balanced equation shows that 2 moles of water produce 1 mole of oxygen, which is essential for calculating the required mass of water.
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Ideal Gas Law

The Ideal Gas Law (PV = nRT) relates the pressure, volume, temperature, and number of moles of a gas. It is crucial for converting the volume of oxygen gas produced into moles, which can then be used in stoichiometric calculations. Understanding this law helps in determining how many moles of O2 correspond to the given conditions of temperature and pressure.
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Molar Mass

Molar mass is the mass of one mole of a substance, typically expressed in grams per mole. It is necessary for converting between moles and grams in stoichiometric calculations. For water (H2O), the molar mass is approximately 18.02 g/mol, which will be used to find the mass of water needed to produce the desired amount of oxygen.
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Related Practice
Textbook Question

Consider the chemical reaction:

C(s) + H2O(g) → CO(g) + H2(g)

How many liters of hydrogen gas are formed from the complete reaction of 22.5 g C? Assume that the hydrogen gas is collected at a pressure of 1.00 atm and a temperature of 355 K.

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Textbook Question

A heliox deep-sea diving mixture contains 2.0 g of oxygen to every 98.0 g of helium. What is the partial pressure of oxygen when this mixture is delivered at a total pressure of 8.5 atm?

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Textbook Question

CH3OH can be synthesized by the reaction: CO(g) + 2 H2(g) → CH3OH( g) What volume of H2 gas (in L), at 748 mmHg and 86 °C, is required to synthesize 25.8 g CH3OH? How many liters of CO gas, measured under the same conditions, are required?

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Textbook Question

Automobile air bags inflate following a serious impact. The impact triggers the chemical reaction: 2 NaN3(s) → 2 Na(s) + 3 N2(g) If an automobile air bag has a volume of 11.8 L, what mass of NaN3 (in g) is required to fully inflate the air bag upon impact? Assume STP conditions.

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Textbook Question

The zinc in a copper-plated penny will dissolve in hydrochloric acid if the copper coating is filed down in several spots (so that the hydrochloric acid can get to the zinc). The reaction between the acid and the zinc is 2 H+(aq) + Zn(s) → H2(g) + Zn2+(aq). When the zinc in a certain penny dissolves, the total volume of gas collected over water at 25 °C is 0.951 L at a total pressure of 748 mmHg. What mass of hydrogen gas is collected?

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Textbook Question

Oxygen gas reacts with powdered aluminum according to the reaction: 4 Al(s) + 3 O2(g) → 2 Al2O3(s) What volume of O2 gas (in L), measured at 782 mmHg and 25 °C, completely reacts with 53.2 g Al?

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