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Chapter 11: Problem 35

a. In a balanced chemical equation, what is the relationship between the molar ratios and the volume ratios of gaseous reactants and products? b. What restriction applies to the use of the volume ratios in solving stoichiometry problems?

Short Answer

Expert verified
a. Molar ratios equal volume ratios for gases under the same conditions. b. Volume ratios can only be used if gases are at the same temperature and pressure.

Step by step solution

01

Understanding Molar Ratios

The molar ratio in a balanced chemical equation represents the proportion of reactants and products in moles. These ratios are derived from the coefficients of each compound in the equation.
02

Relationship Between Molar and Volume Ratios

For gaseous reactants and products, the volumes of gases are directly proportional to the number of moles. Hence, the molar ratios of gases in a balanced equation are also the volume ratios under the same conditions of temperature and pressure.
03

Understanding Volume Ratios

Volume ratios of gaseous reactants and products can be used in stoichiometry calculations because one mole of any gas at the same temperature and pressure occupies the same volume. This means that if the temperature and pressure are constant, the volume ratios will equal the molar ratios.
04

Restriction on Using Volume Ratios

The restriction on using volume ratios in solving stoichiometry problems is that the gases must be measured under the same conditions of temperature and pressure. If these conditions vary, the volume ratios will no longer be proportional to the molar ratios.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Molar Ratios
Molar ratios are essential when studying chemical reactions. In a balanced chemical equation, molar ratios show how much of each substance is needed or produced. They come from the coefficients in the balanced equation.
For example, in the equation 2H₂ + O₂ → 2H₂O these coefficients (2 for H₂ and H₂O, 1 for O₂) tell us that 2 moles of hydrogen gas react with 1 mole of oxygen gas to form 2 moles of water gas.
Molar ratios help us calculate how much of a reactant is needed to fully react with another, or how much product will be made from set amounts of reactants.
Volume Ratios
Volume ratios are particularly useful when dealing with gases. Just like molar ratios, volume ratios represent the relationship between the volumes of gaseous reactants and products. This is possible because, under the same conditions of temperature and pressure, equal volumes of gases contain the same number of molecules (according to Avogadro's law).
Let's revisit our equation: 2H₂ + O₂ → 2H₂O If the gases are at the same temperature and pressure, 2 volumes of hydrogen will react with 1 volume of oxygen to produce 2 volumes of water vapor. This means the volume ratio of H₂ : O₂ : H₂O is also 2:1:2.
Stoichiometry
Stoichiometry is the branch of chemistry that deals with the relative quantities of reactants and products in chemical reactions. It relies heavily on balanced chemical equations to determine these amounts.
Whether calculating moles, mass, or gas volumes, stoichiometry helps make sense of the quantities involved. For gas reactions, we use molar and volume ratios to predict how much of each gas is required or produced. Always remember:
  • Use the coefficients of a balanced equation for molar ratios.
  • Volume ratios can be used if gases are measured under the same conditions.
Temperature and Pressure Conditions
Understanding the conditions of temperature and pressure is crucial when dealing with gas calculations in stoichiometry. To accurately use volume ratios, the gases must be under the same temperature and pressure.
For instance, at standard temperature and pressure (STP, which is 0°C and 1 atmosphere), one mole of any gas occupies 22.4 liters. If these conditions change, the volume a gas occupies will also change, altering the ratio.
Therefore, always ensure:
  • Gases are compared under the same conditions of temperature and pressure.
  • If conditions differ, recalculate the volumes using the ideal gas law if necessary.
This ensures the ratios remain accurate and the calculations reliable.

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Most popular questions from this chapter

State the assumptions that the kinetic-molecular theory makes about the characteristics of gas particles.

How many moles of helium gas would it take to fill a balloon with a volume of 1000.0 \(cm^{3}\) when the temperature is \(32^{\circ} C\) and the atmospheric pressure is 752 \(mm\) Hg?

A flask containing 155 \(cm^{3}\) of hydrogen was collected under a pressure of 22.5 \(kPa\) . What pressure would have been required for the volume of the gas to have been \(90.0 cm^{3},\) assuming the same temperature?

Explain the processes involved in the liquefaction of gases. Name some substances that are gases under normal room conditions and that are typically used in the liquid form. Explain why this is so.

Assume that 5.60 \(LH_{2}\) at STP reacts with excess \(CuO\) according to the following equation: $$CuO(s)+H_{2}(g) \rightarrow Cu(s)+H_{2} O(g)$$ Make sure the equation is balanced before beginning your calculations. a. How many moles of \(H_{2}\) react? b. How many moles of \(Cu\) are produced? c. How many grams of \(Cu\) are produced?
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