Chemistry Chapter: Conservation and Conversions

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Questions and Answers

What defines a limiting reactant in a chemical reaction?

  • It is the reactant that limits the reaction. (correct)
  • It is the reactant that participates in side reactions.
  • It is the substance formed during the reaction.
  • It is the reactant that is present in excess.

Which statement regarding excess reactants is true?

  • Excess reactants do not contribute to the formation of products.
  • Excess reactants can limit the yield of a product.
  • Excess reactants are always consumed completely in the reaction.
  • Excess reactants are present in greater quantities than limiting reactants. (correct)

What is the theoretical yield in a chemical reaction?

  • The actual amount of product obtained from the reaction.
  • The ratio of actual yield to theoretical yield.
  • The actual yield adjusted for impurities.
  • The maximum amount of product that can be produced from given reactants. (correct)

How is percentage yield calculated?

<p>By dividing actual yield by theoretical yield and multiplying by 100. (C)</p> Signup and view all the answers

When might the experimental yield be lower than the theoretical yield?

<p>When side reactions occur during the process. (A)</p> Signup and view all the answers

In a reaction, if the actual yield is 2.5 grams and the theoretical yield is 5 grams, what is the percentage yield?

<p>50% (B)</p> Signup and view all the answers

Which formula represents the calculation of percentage yield?

<p>Percentage Yield = (actual yield / theoretical yield) × 100 (C)</p> Signup and view all the answers

What is a product in a chemical reaction?

<p>A substance that is formed during the reaction. (D)</p> Signup and view all the answers

What is the number of moles of NaCl used in the reaction?

<p>0.03 mol (B)</p> Signup and view all the answers

How much aluminum (Al) is left over after the reaction?

<p>0.1 mol (D)</p> Signup and view all the answers

What is the limiting reactant in this chemical reaction?

<p>NaCl (B)</p> Signup and view all the answers

What is the total molar mass of AlCl3?

<p>132 g/mol (D)</p> Signup and view all the answers

How many grams of AlCl3 are formed in the reaction?

<p>3.41 g (B)</p> Signup and view all the answers

Which calculation is performed to find the number of moles of Al?

<p>Dividing grams of Al by its molar mass (D)</p> Signup and view all the answers

What is the relationship between the amount of moles of NaCl and AlCl3 produced?

<p>3:1 ratio (B)</p> Signup and view all the answers

What would increase the amount of AlCl3 produced?

<p>Increasing NaCl concentration (D)</p> Signup and view all the answers

Which of the following statements is true regarding the calculation of limiting reactants?

<p>Limiting reactants are calculated based on stoichiometric ratios. (C)</p> Signup and view all the answers

What does the law of conservation of matter state?

<p>The amount of matter remains constant before and after a reaction. (D)</p> Signup and view all the answers

In the equation 4NH3 + 3O2 = 2N2 + 6H2O, how many moles of O2 are required to react with 8 moles of NH3?

<p>6 moles O2 (C)</p> Signup and view all the answers

Which of the following best describes a limiting reagent?

<p>The reactant that is fully consumed in a chemical reaction. (A)</p> Signup and view all the answers

What is the purpose of a balanced chemical equation?

<p>To convey the proportions of reactants and products involved. (C)</p> Signup and view all the answers

What is percent yield?

<p>The ratio of actual yield to theoretical yield multiplied by 100. (C)</p> Signup and view all the answers

In a mole-to-mole conversion, which factor is used to determine the number of moles of a reactant?

<p>The coefficients in the balanced chemical equation. (C)</p> Signup and view all the answers

Which of the following is true about excess reagents?

<p>They remain unreacted after the reaction is complete. (B)</p> Signup and view all the answers

How many moles of NH3 are present if 12 moles of O2 react according to the equation 4NH3 + 3O2 = 2N2 + 6H2O?

<p>16 moles NH3 (C)</p> Signup and view all the answers

What unit is most commonly used to measure reactants or products in a laboratory?

<p>Grams (D)</p> Signup and view all the answers

What is required to convert moles to grams?

<p>The molar mass of the substance (B)</p> Signup and view all the answers

How many moles of O2 are needed to react with 8 moles of NH3 according to the balanced chemical equation?

<p>6 moles (D)</p> Signup and view all the answers

What is the molar mass of O2 from the given information?

<p>31.8 g/mol (A)</p> Signup and view all the answers

Which of the following steps involves changing grams of NH3 to moles?

<p>Step 3 (A)</p> Signup and view all the answers

In the reaction involving NH3 and O2, how many grams of O2 are needed to react with 250 g of NH3?

<p>42.8 g (B)</p> Signup and view all the answers

What is the first step in solving a mass-to-mass conversion problem?

<p>Conversion of grams to moles of the first substance (D)</p> Signup and view all the answers

Which conversion factor is used to relate NH3 to O2 in the reaction?

<p>4 moles NH3 to 3 moles O2 (A)</p> Signup and view all the answers

To find the reactants that produce the maximum quantity of products at minimum cost, what is essential?

<p>Balancing the chemical equation (C)</p> Signup and view all the answers

When converting moles to grams, what is the last step?

<p>Use the molar mass to convert to grams (D)</p> Signup and view all the answers

What does 15.9 u represent in this context?

<p>The average atomic mass of oxygen (A)</p> Signup and view all the answers

If 250 g of NH3 are used, how many grams of O2 can be produced?

<p>42.8 g (C)</p> Signup and view all the answers

What happens to the number of moles of O2 when moles of NH3 are increased?

<p>Moles of O2 increase (C)</p> Signup and view all the answers

What is the purpose of using a balanced chemical equation in mole-to-mass conversions?

<p>To ensure the conservation of mass (A)</p> Signup and view all the answers

Flashcards

Conservation of Matter

The principle that the total amount of matter remains constant during a chemical reaction.

Mole-to-Mole Conversion

Using the ratio of moles between substances in a balanced chemical equation to determine the number of moles of one substance given the moles of another.

Balanced Chemical Equation

A chemical equation representing a reaction with equal numbers of atoms of each element on both sides of the equation.

Conversion Factor

A ratio used to convert from one unit to another, often derived from the balanced chemical equation.

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Limiting Reactant

The reactant that is completely consumed in a chemical reaction, limiting the amount of product that can form.

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Excess Reactant

The reactant that is not completely consumed in a chemical reaction.

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Mole

A unit of measurement representing approximately 6.02 x 10^23 particles (atoms, molecules, etc.).

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Theoretical Yield

The maximum amount of product that can be formed from a given amount of reactant.

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Percent Yield

The ratio of the actual yield of a product to the theoretical yield, expressed as a percentage.

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Mole-to-Mass Conversion

Converting the amount of a substance from moles to grams or vice-versa using molar mass.

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Molar Mass

The mass of one mole of a substance, expressed in grams per mole (g/mol).

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Mole Ratio

The ratio of the coefficients of two substances in a balanced chemical equation, representing their relative amounts in the reaction.

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Unit Analysis

A problem-solving method that uses the units of measurements to guide calculations and conversions.

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Reactant

A substance that takes part in and undergoes change during a reaction.

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Product

A substance produced in a chemical reaction.

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Chemical Equation

A symbolic representation of a chemical reaction in the form of chemical formulas and coefficients.

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Coefficient

A number placed in front of a chemical formula in a chemical equation to indicate the relative number of moles of that substance.

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Atomic Mass

The mass of an atom of a chemical element.

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Molecular Mass

The mass of a molecule relative to the mass of a carbon-12 atom.

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Chemical Formula

A representation of the elements present in a compound and their relative ratios.

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Actual Yield

The amount of product you actually get in a real-world lab experiment.

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How to determine the limiting reactant?

To find the limiting reactant, compare the number of moles of each reactant needed for the reaction to occur completely. The reactant with the fewer moles needed is the limiting reactant.

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How to calculate the excess reactant?

After determining the limiting reactant, use the stoichiometry of the balanced equation to calculate how much of the excess reactant is used up. Subtract that from the initial amount to find the remaining excess reactant.

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How to calculate the theoretical yield?

Once you know which reactant is limiting, use the stoichiometry of the balanced equation to calculate the maximum amount of product you can make from that limiting reactant.

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How to identify the limiting reactant?

Compare the calculated moles of each reactant after dividing by their respective coefficients in the balanced chemical equation. The reactant with the smallest calculated value is the limiting reactant.

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Calculating excess reactant

Subtract the moles of the limiting reactant from the initial moles of the excess reactant.

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Calculating product yield

Use stoichiometry to calculate the mass of product formed based on the moles of the limiting reactant.

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What is stoichiometry?

The study of the quantitative relationships between reactants and products in chemical reactions. It involves using mole ratios to determine the amount of reactants and products.

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Gram-to-Mole Conversion

Converting the mass of a substance from grams to moles or vice-versa using molar mass.

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Study Notes

Conservation of Matter

  • Chemical equations are useful for interpreting chemical reactions.
  • Students will learn how to calculate percent yield and theoretical yield.
  • Students will learn to identify limiting and excess reagents.
  • The law of conservation of mass (or matter) states that the amount of matter before and after a reaction remains the same.

Mole-to-Mole Conversion

  • The number of moles of a substance in a chemical reaction can be determined if the number of moles of another substance is known.
  • Mole conversion factors are based on the coefficients in a balanced chemical equation.
  • Example: 4NH₃ + 3Oâ‚‚ → 2Nâ‚‚ + 6Hâ‚‚O

Mole-to-Mass Conversion

  • Grams are a convenient unit for measuring reactants and products in a lab.
  • To convert between moles and grams, use the molar mass of the substance.
  • Example: How many grams of Oâ‚‚ are needed to react with 8 moles of NH₃?

Mass-to-Mass Conversion

  • This conversion is used when the mass of one substance is known, and the mass of another substance is needed.
  • Example: How many grams of Oâ‚‚ are needed to react with 250 g of NH₃?

Reaction Yield

  • Theoretical yield: maximum amount of product possible.
  • Actual yield: amount of product obtained in a lab.
  • Percentage yield: efficiency of a reaction, calculated as (actual yield / theoretical yield) * 100.
  • Limiting reactant: reactant that limits the amount of product.
  • Excess reactant: reactant present in excess of the limiting reactant.

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Conservation of Matter Lesson 7-8 PDF

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