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Ch.6 - Gases
Chapter 6, Problem 101

Consider the reaction: 2 NiO(s) → 2 Ni(s) + O2(g). If O2 is collected over water at 40.0 °C and a total pressure of 745 mmHg, what volume of gas is collected for the complete reaction of 24.78 g of NiO?

Verified step by step guidance
1
Calculate the molar mass of NiO by adding the atomic masses of Ni and O.
Determine the number of moles of NiO by dividing the given mass (24.78 g) by the molar mass of NiO.
Use the stoichiometry of the balanced chemical equation to find the moles of O2 produced. According to the equation, 2 moles of NiO produce 1 mole of O2.
Use the ideal gas law, PV = nRT, to calculate the volume of O2. First, convert the temperature from Celsius to Kelvin by adding 273.15.
Adjust the total pressure to account for the vapor pressure of water at 40.0 °C, then use the adjusted pressure in the ideal gas law to find the volume of O2.

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 amount of product formed or reactant consumed from a given quantity of another substance. In this case, we need to use the molar ratios from the balanced equation to find out how much O2 is produced from the decomposition of NiO.
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Gas Laws

Gas laws describe the behavior of gases in relation to pressure, volume, and temperature. The Ideal Gas Law (PV=nRT) is particularly useful for calculating the volume of gas produced under specific conditions. In this scenario, we will apply the gas laws to determine the volume of O2 collected, taking into account the total pressure and the vapor pressure of water at 40.0 °C.
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Vapor Pressure of Water

The vapor pressure of water is the pressure exerted by water vapor in equilibrium with its liquid at a given temperature. At 40.0 °C, the vapor pressure of water must be subtracted from the total pressure to find the partial pressure of the O2 gas collected. This adjustment is crucial for accurately calculating the volume of O2 produced in the reaction.
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