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Chapter 11: Problem 56

On what law is stoichometry based, and how do the calculations support this law?

Short Answer

Expert verified
Stoichiometry is based on the Law of Conservation of Mass, which states that mass cannot be created or destroyed in a chemical reaction. Stoichiometric calculations use balanced chemical equations to ensure the conservation of mass in the reaction. They can be used to determine the amount of product formed, calculate the limiting reactant, and calculate the percent yield of a reaction. These calculations maintain the relationships between the molar amounts of reactants and products, thus supporting the Law of Conservation of Mass.

Step by step solution

01

Identify the law behind stoichiometry

Stoichiometry is based on the Law of Conservation of Mass, which states that mass cannot be created or destroyed in a chemical reaction. In other words, the total mass of the reactants in a chemical reaction must be equal to the total mass of the products.
02

Explain how stoichiometric calculations support the Law of Conservation of Mass

Stoichiometric calculations involve using the balanced chemical equation of a reaction to determine the amounts of reactants and products involved. In a balanced chemical equation, the number of atoms of each element on both sides of the equation must be equal. This ensures the conservation of mass in the reaction, as the total mass of reactants will always be equal to the total mass of products. These calculations can be used to: 1. Determine the amount of product formed from a given amount of reactants. 2. Calculate the limiting reactant in a reaction, which is the reactant that runs out first and thereby limits the amount of product that can be formed. 3. Calculate the percent yield of a reaction, which is the ratio of the actual yield (amount of product obtained from the reaction) to the theoretical yield (amount of product calculated from stoichiometry). All of these calculations are based on the relationships between the molar amounts of reactants and products in a balanced chemical equation, which helps ensure the Law of Conservation of Mass is upheld in chemical reactions.

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Key Concepts

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

Law of Conservation of Mass
The Law of Conservation of Mass is a fundamental principle in chemistry stating that mass is neither created nor destroyed during a chemical reaction. Antoine Lavoisier first discovered this crucial concept in the 18th century. Due to this law, the total mass of the reactants in a reaction is always equal to the total mass of the products. This balance ensures that every atom appearing in the reactants will also appear in the products, simply rearranged to form new substances.
  • In any chemical reaction, no atoms are lost or gained, only rearranged.
  • The law forms the basis for stoichiometry, which involves quantitative relationships in chemical reactions.
  • Understanding this principle is key to predicting the outcome of chemical reactions accurately.
By using this law, chemists can ensure reactions are correctly balanced, allowing for accurate predictions and calculations in experiments.
Balanced Chemical Equation
A balanced chemical equation represents the mole ratios of reactants and products in a chemical reaction, ensuring the Law of Conservation of Mass is respected. When a chemical equation is balanced, the number of each type of atom is the same on both sides of the equation. Achieving a balanced equation:
- Involves adding appropriate coefficients to the chemical formulas so that all elements have the same number of atoms on the reactant and product sides.- Ensures stoichiometry works by providing accurate information about the proportions of substances involved.For example, in the combustion of methane:\[ \text{CH}_4 + 2\text{O}_2 \rightarrow \text{CO}_2 + 2\text{H}_2\text{O} \]This equation is balanced as it shows 1 carbon (C) atom from methane forming carbon dioxide and 4 hydrogen (H) atoms forming water, with enough oxygen (O) to satisfy both products. Balanced equations are essential tools for chemists, allowing them to calculate the exact amounts of substances needed or produced in a reaction.
Limiting Reactant
In a chemical reaction, the limiting reactant is the one that is completely consumed first, limiting the amount of products formed. This concept helps in determining how much product a reaction can produce before stopping. Identifying the limiting reactant involves comparing the amount of reactants available to the amounts needed according to the balanced chemical equation.
  • To find the limiting reactant, calculate the number of moles of each reactant and use the balanced chemical equation to determine which will be depleted first.
  • The reactant present in lesser quantity, when calculated using stoichiometric ratios, is the limiting reactant.
  • Once identified, the limiting reactant determines the maximum yield of the products.
Understanding the limiting reactant is vital for optimizing reaction conditions, as it can guide the proportion of materials used to avoid waste and enhance efficiency.
Percent Yield
Percent yield is a metric used in chemistry to assess the efficiency of a reaction. It compares the actual yield obtained from an experiment to the theoretical yield predicted by stoichiometry. The formula used to calculate percent yield is:\[ \text{Percent Yield} = \left( \frac{\text{Actual Yield}}{\text{Theoretical Yield}} \right) \times 100 \]This calculation provides vital information regarding the effectiveness of a reaction and highlights any possible experimental errors or inefficiencies.
- A percent yield of 100% indicates that the reaction was perfectly efficient, with all reactants converting to products as expected.- Values below 100% suggest inefficiencies, possibly due to side reactions, incomplete reactions, or loss of product during handling.- Scientists use this information to improve reaction conditions and minimize waste.Calculating percent yield is essential for verifying whether a reaction proceeds as planned and for confirming the accuracy of stoichiometric predictions.

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Most popular questions from this chapter

List several reasons why the actual yield from a chemical reaction is not usually equal to the theoretical yield.

Solid silicon dioxide, often called silica, reacts with hydrofluoric acid (HF) solution to produce the gas silicon tetrafluoride and water. a. Write the balanced chemical equation for the reaction. b. List three mole ratios, and explain how you would use them in stoichiometric calculations.

Air Pollution Research the air pollutants produced by combustion of gasoline in internal combustion engines. Discuss the common pollutants and the reaction that produces them. Show, through the use of stoichiometry, how each pollutant could be reduced if more people used mass transit.

Hydrofluoric acid solutions cannot be stored in glass containers because HF reacts readily with silica dioxide in glass to produce hexafluorosilicic acid ( \(\mathrm{H}_{2} \mathrm{SiF}_{6}\) ). $$\mathrm{SiO}_{2}(\mathrm{~s})+6 \mathrm{HF}(\mathrm{aq}) \rightarrow \mathrm{H}_{2} \mathrm{SiF}_{6}(\mathrm{aq})+2 \mathrm{H}_{2} \mathrm{O}(\mathrm{l})$$ \(40.0 \mathrm{~g} \mathrm{SiO}_{2}\) and \(40.0 \mathrm{~g} \mathrm{HF}\) react to yield \(45.8 \mathrm{~g} \mathrm{H}_{2} \mathrm{SiF}_{6}\) a. What is the limiting reactant? b. What is the mass of the excess reactant? c. What is the theoretical yield of \(\mathrm{H}_{2} \mathrm{SiF}_{6} ?\) d. What is the percent yield?

Car Battery Car batteries use lead, lead(IV) oxide, and a sulfuric acid solution to produce an electric current. The products of the reaction are lead(II) sulfate in solution and water. a. Write the balanced equation for the reaction. b. Determine the mass of lead(II) sulfate produced when 25.0 g of lead reacts with an excess of lead(IV) oxide and sulfuric acid.
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