Stoichiometry & Chemical Reactions Quiz

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Questions and Answers

What occurs when NaOH dissolves in water?

  • NaOH reacts with water to produce gas.
  • NaOH does not dissociate in water.
  • NaOH forms sodium ions and hydroxide ions in solution. (correct)
  • NaOH forms a precipitate when mixed with water.

Which of the following statements is true regarding the solubility of ionic compounds?

  • All carbonates are soluble in water.
  • Silver chloride is an example of an insoluble compound. (correct)
  • Potassium nitrate is insoluble in water.
  • All nitrates are insoluble in water.

What type of reaction occurs when an acid neutralizes a base?

  • Precipitation reaction
  • Acid-base reaction (correct)
  • Redox reaction
  • Combustion reaction

Which situation would most likely result in no reaction when mixing ionic solutions?

<p>Mixing solutions with ions that remain in solution. (A)</p> Signup and view all the answers

What is the correct classification of a reaction that absorbs heat?

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

Which of the following ions is always soluble in water?

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

What is the heat of combustion?

<p>The heat released in a combustion reaction. (D)</p> Signup and view all the answers

Which of the following statements accurately reflects the behavior of precipitation reactions?

<p>They create an insoluble solid from ionic solutions. (B)</p> Signup and view all the answers

What determines the limiting reactant in a chemical reaction?

<p>The reactant present in the smallest stoichiometric amount (C)</p> Signup and view all the answers

How do you calculate the percent composition of an element in a compound?

<p>By multiplying the number of atoms by the atomic weight and dividing by the molecular weight of the compound (B)</p> Signup and view all the answers

What happens when reactants are mixed in proportions that do not match the balanced equation?

<p>One reactant will remain unreacted (C)</p> Signup and view all the answers

If you have 4 moles of NH3 in the reaction 4NH3 + 5O2 --> 6H2O + 4NO, how many grams of H2O are produced?

<p>59.5 g (D)</p> Signup and view all the answers

What is the molecular weight of ethane (C2H6)?

<p>30.0 amu (C)</p> Signup and view all the answers

In the reaction 4NH3 + 5O2 --> 6H2O + 4NO, what is the number of moles of O2 required to produce 0.6 moles of H2O?

<p>0.8 moles (B)</p> Signup and view all the answers

If 15 moles of H2O is produced in the reaction 4NH3 + 5O2 --> 6H2O + 4NO, how many grams of NO are produced?

<p>10 g (D)</p> Signup and view all the answers

How many moles of H2O can be produced from 3.5 moles of O2 in the reaction 4NH3 + 5O2 --> 6H2O + 4NO?

<p>4.2 moles (A)</p> Signup and view all the answers

When calculating the moles of a substance, what is the common mistake made in the equation mole = gram + molecular weight?

<p>Adding instead of dividing molecular weight (A)</p> Signup and view all the answers

If you were to combine 2.5 moles of NH3 with excess oxygen, how many grams of NO will be produced according to the reaction 4NH3 + 5O2 --> 6H2O + 4NO?

<p>18.9 g (B)</p> Signup and view all the answers

In a reaction, if the limiting reactant is 2 moles of H2, how will it affect the amount of product formed?

<p>Decrease the product yield (A)</p> Signup and view all the answers

Flashcards

Moles

The number of moles of a substance is directly proportional to the number of molecules of that substance. 1 mole of any substance contains Avogadro's number (6.022 x 10^23) of molecules.

Stoichiometric Calculations

The ratio of the coefficients of two substances in a balanced chemical equation represents the mole ratio between them. This ratio can be used to calculate the amount of one substance produced or consumed given the amount of another substance.

Limiting Reactant

The amount of product formed in a chemical reaction is limited by the reactant that gets completely consumed first. This reactant is called the limiting reactant.

Molecular Weight

The molecular weight of a molecule is the sum of the atomic weights of all atoms in the molecule. It is expressed in atomic mass units (amu).

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Percent Composition

The percent composition of a compound refers to the percentage by mass of each element present in the compound.

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Heat of Reaction

The heat change accompanying a chemical reaction is called the heat of reaction. It can be either positive (endothermic, heat absorbed) or negative (exothermic, heat released).

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Predicting Ion Reactions in Aqueous Solution

The reaction between ions in an aqueous solution is determined by the solubility rules and the formation of precipitates. If the reaction results in the formation of an insoluble compound (precipitate), then the ions will react.

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Theoretical and Actual Yield

The theoretical yield is the maximum amount of product that can be formed from a given amount of reactants, assuming 100% efficiency. The actual yield is the amount of product that is actually obtained from a reaction.

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Percent Yield

The amount of product obtained from a chemical reaction, expressed as a percentage of the theoretical yield.

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Theoretical Yield

The theoretical maximum amount of product that can be formed from a given amount of reactants, assuming 100% efficiency.

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Percent Yield

The ratio of the actual yield to the theoretical yield, multiplied by 100%.

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Limiting Reactant Problem

A chemical reaction where the reactants are not in the stoichiometric ratio needed for complete conversion, resulting in some reactants being left over.

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Molar Mass

The mass of a substance that contains 6.022 x 10^23 particles (atoms, molecules, or ions).

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Dissociation

The process where ions in a solution break apart from each other due to the interaction with water molecules. For example, when NaOH dissolves in water, it forms Na+ and OH- ions.

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Precipitation Reaction

A chemical reaction where two ions combine to form an insoluble solid that falls out of solution. An example is mixing AgNO3 and NaCl to form AgCl precipitate.

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Gas Evolution Reaction

A chemical reaction where two ions combine to form a gas that bubbles out of the solution. For example, adding baking soda (NaHCO3) to acid produces carbon dioxide gas.

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Neutralization reaction

A reaction between an acid and a base, typically forming water and a salt. For example, HCl (acid) reacting with NaOH (base) produces NaCl (salt) and H2O.

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Redox Reaction

A chemical reaction where electrons are transferred between reactants. For example, the reaction of copper with silver ions (Ag+) results in copper ions (Cu2+) and metallic silver.

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Heat of Combustion

The amount of heat released during a combustion reaction. For example, burning fuels like propane releases heat, which is the heat of combustion of that fuel.

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Endothermic Reaction

A reaction that absorbs heat from the surroundings, causing the reaction mixture to get colder. For example, dissolving some salts in water can be endothermic.

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Study Notes

Stoichiometry & Chemical Reactions in Aqueous Solution

  • Learning Objectives: Students will be able to:
    • Solve stoichiometric problems
    • Calculate percent composition
    • Understand limiting reactants
    • Understand heat of reaction
    • Predict if ions react in aqueous solutions

Moles and Molecular Scale

  • Moles provide a connection between molecular and macroscopic scales.
  • One mole of any substance contains the same number of molecules.
  • Avogadro's number (approximately 6.022 x 1023) represents the number of molecules in one mole.
  • Mole calculations involve converting between grams, moles, and molecules.

Example Calculation

  • Given the reaction 2H2 + O2 → 2H2O:
    • 2 molecules of H2 + 1 molecule of O2 produce 2 molecules of H2O.
    • 4.0 amu H2 + 32.0 amu O2 produce 36.0 amu H2O
    • 2 moles H2 + 1 mole O2 produce 2 moles H2O.
    • 4.0 g H2 + 32.0 g O2 produce 36.0 g H2O.

Further Calculations

  • Reaction: 4NH3 + 5O2 → 6H2O + 4NO
    • If 15 moles of H2O are produced, 10 moles of NO are produced.
    • If 2.2 moles of NH3 react, 3.3 moles of H2O are produced (approximately 59.47 g).

Molecular Weight

  • Molecular weight is the sum of the atomic weights of all atoms in a molecule.
  • For example, the molecular weight of ethane (C2H6) is approximately 30.0 amu.
    • (2 * 12.0 amu) + (6 * 1.01 amu)

Determining O2 Needed for Reaction

  • For the reaction 4NH3 + 5O2 → 6H2O + 4NO:
    • 0.3 moles of H2O require 0.25 moles of O2 (approximately 8g).

Stoichiometric Calculations

  • Use balanced chemical equations to determine quantities of reactants and products.
  • Using molar masses and stoichiometric ratios, calculate quantities in grams.
    • Gram → mole → mole → Gram

Limiting Reactants

  • The limiting reactant determines the maximum amount of product possible.
  • If the reactants are not mixed in their stoichiometric ratio, one reactant will be consumed completely, limiting the product yield

Identifying Limiting Reactants

  • In the reaction HCl + NaOH → H2O + NaCl:
    • Using the correct coefficients in the balanced reaction helps determine the limiting reactant and the amount of product formed.

Percent Composition

  • The percentage of each element in a compound is determined by comparing the element's mass to the total molecular mass.
  • The formula is: (number of atoms × atomic weight)/molecular weight × 100%
    • e.g., calculating %C and %H in ethane (C2H6).

Predicting Ion Reactions in Aqueous Solutions

  • Many ionic compounds dissolve in water, dissociating into ions.
  • Predicting if ions react depends on the formation of insoluble solids (precipitate), gases or neutralisation reactions.
    • Reactions like NaOh + H2O = Na+ + OH-

Important Solubility Rules

  • Common ionic compounds with Na+, K+, and NHâ‚„+ are soluble in water.
  • Most nitrates and acetates are soluble.
  • Most chlorides and sulfates are soluble, with exceptions.
  • Most carbonates, phosphates, sulfides, and hydroxides are insoluble, with exceptions.

Heat of Reaction

  • The heat absorbed or released during a reaction is the heat of reaction.
  • Exothermic reactions release heat (e.g., combustion).
  • Endothermic reactions absorb heat.

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