Stoichiometry and Chemical Equations Class 10

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Questions and Answers

What characterizes a combination reaction?

One reactant absorbs energy from the surroundings.

Two or more substances react to form two products.

A single reactant decomposes into multiple products.

Two or more substances react to form one product. (correct)

Which of the following equations represents a combination reaction?

2 Na + Cl2 ⎯⎯→ 2 NaCl (correct)

CaCO3 ⎯⎯→ CaO + CO2

2 H2 + O2 ⎯⎯→ 2 H2O (correct)

3 CO2 ⎯⎯→ 3 C + 3 O2

Which of these is not an example of a combination reaction?

2 Mg + O2 ⎯⎯→ 2 MgO

C3H6 + Br2 ⎯⎯→ C3H6Br2

N2 + 3 H2 ⎯⎯→ 2 NH3

2 H2O ⎯⎯→ 2 H2 + O2 (correct)

In the reaction N2 + 3 H2 ⎯⎯→ 2 NH3, how many molecules of hydrogen are required for the reaction?

3 molecules Signup and view all the answers

What is a common feature of all combination reactions?

They result in the formation of a single product. Signup and view all the answers

What is the correct interpretation of the reaction 2H2 + O2 ⟶ 2H2O?

Two molecules of hydrogen react with one molecule of oxygen to produce two molecules of water. Signup and view all the answers

What does the term 'amu' stand for in the context of formula weights?

Atomic mass unit, defined as 1/12 of the mass of the 12C isotope. Signup and view all the answers

In the combustion reaction CH4 + 2 O2 ⟶ CO2 + 2 H2O, which statement is true?

The coefficients indicate the moles of each compound involved in the reaction. Signup and view all the answers

Which statement accurately reflects the stoichiometry of the reaction C3H8 + 5 O2 ⟶ 3 CO2 + 4 H2O?

One mole of propane reacts completely with five moles of oxygen. Signup and view all the answers

What reaction type is represented by the equation 2H2 + O2 ⟶ 2H2O?

Synthesis reaction. Signup and view all the answers

What is the number of moles of NH3 when it is the limiting reagent with 1.5g available?

0.088 mol Signup and view all the answers

When using 2.75g of a reactant with a molar mass of 32g/mol, how many moles does this correspond to?

0.086 mol Signup and view all the answers

If O2 is the limiting reagent, what would be the moles of NH3 produced from 0.086 mol O2?

0.069 mol Signup and view all the answers

What is the molar mass of the reactant if 2.1g corresponds to 0.1 mol?

30 g/mol Signup and view all the answers

What is the resulting moles of the product if 1.8g of a reactant with a molar mass of 18g/mol is reacted?

0.1 mol Signup and view all the answers

What information is represented in parentheses next to each compound in a chemical equation?

The states of the reactants and products Signup and view all the answers

In the chemical equation CH4 (g) + 2 O2 (g) → CO2 (g) + 2 H2O (g), what is the total number of oxygen molecules on the reactants side?

2 Signup and view all the answers

Which compound serves as a product in the given chemical equation?

CO2 (g) Signup and view all the answers

How many hydrogen atoms are produced in the reaction CH4 (g) + 2 O2 (g) → CO2 (g) + 2 H2O (g)?

4 Signup and view all the answers

Which statement about the stoichiometry of the reaction is true?

The number of moles of reactants equals the number of moles of products. Signup and view all the answers

What is the role of Avogadro's number in relation to moles?

It defines the number of particles in one mole. Signup and view all the answers

How is the percentage of oxygen in a compound determined through combustion analysis?

It is calculated by the difference after determining the percentages of carbon and hydrogen. Signup and view all the answers

Given a compound with 61.31% carbon, 5.14% hydrogen, 10.21% nitrogen, and 23.33% oxygen, what is the first step in determining its empirical formula?

Convert the mass percentages directly to moles. Signup and view all the answers

What is the primary use of combustion analysis in chemistry?

To derive the elemental composition of a compound containing carbon, hydrogen, and oxygen. Signup and view all the answers

If a compound contains 10.21% nitrogen, which process would most likely provide the nitrogen's percentage accurately?

Calculation by subtracting the percentages of carbon and hydrogen from the total mass. Signup and view all the answers

How many atomic mass units (amu) does a single carbon-12 ($^{12}C$) atom weigh?

12 amu Signup and view all the answers

What is the relationship between grams and atomic mass units for 12C atoms?

1 amu is equivalent to 1.6605 x 10^-24 g Signup and view all the answers

If 6.022 x 10^23 $^{12}C$ atoms weigh 12 g, how much would 1 $^{12}C$ atom weigh in grams?

1.992 x 10^-23 g Signup and view all the answers

What does the value 6.022 x 10^23 represent in the context of $^{12}C$?

The number of atoms in one mole of any substance Signup and view all the answers

How do you calculate the number of $^{12}C$ atoms that would weigh 12 g?

Divide the total mass by the atomic mass of $^{12}C$. Signup and view all the answers

Study Notes

Stoichiometry: Calculations with Chemical Formulas and Equations

Stoichiometry is the calculation of reactants and products in a chemical reaction.
The Law of Conservation of Mass states that matter is neither created nor destroyed in a chemical reaction. The total mass of the reactants equals the total mass of the products.

3.1: Chemical Equations

A chemical equation represents a chemical reaction.
Reactants are on the left side of the equation.
Products are on the right side of the equation.
The states of reactants and products are written in parentheses to the right of the compound. For example, (g) for gas, (l) for liquid, (s) for solid.
Coefficients are inserted to balance the equation. The number of atoms of each element on the reactant side should equal the number of atoms of each element on the product side.

Subscripts and Coefficients

Subscripts indicate the number of atoms of each element in a molecule.
Coefficients indicate the number of molecules (compounds).

3.2: Some Simple Patterns of Chemical Reactivity

Combination Reactions: Two or more substances react to form one product.
- Examples: N₂ + 3H₂ → 2NH₃, 2Mg + O₂ → 2MgO
Decomposition Reactions: One substance breaks down into two or more substances.
- Examples: CaCO₃ → CaO + CO₂, 2KClO₃ → 2KCl + 3O₂
Combustion Reactions: Rapid reactions with oxygen as a reactant. Hydrocarbons often react with oxygen to form CO₂ and H₂O.
- Examples: CH₄ + 2O₂ → CO₂ + 2H₂O, C₃H₈ + 5O₂ → 3CO₂ + 4H₂O

3.3: Formula Weights

Formula weight (FW): The sum of the atomic weights of the atoms in a chemical formula.
This is generally reported for ionic compounds.
For example, the formula weight of CaCl₂ is calculated by adding the atomic weight of Calcium (Ca) and twice the atomic weight of Chlorine (Cl).

3.4: Avogadro's Number and the Mole

The amu (atomic mass unit) is defined as 1/12 the mass of a carbon-12 atom. 1 amu = 1.6605 x 10⁻²⁴ g
Avogadro's number (6.022 x 10²³): The number of atoms or molecules in one mole of a substance.
A mole is a convenient unit for counting atoms or molecules. One mole of any substance has the same number of particles (atoms or molecules) as one mole of any other substance.
Molar mass: The mass in grams of one mole of a substance. The molar mass of a substance is numerically equal to its formula weight, but expressed in grams per mole (g/mol).

3.5: Finding Empirical Formulas

Combustion analysis: A method typically used to determine the percent composition of a compound containing carbon, hydrogen, and oxygen.
By measuring the mass of CO₂ and H₂O produced when the compound is burned in oxygen, the percent composition of a sample can be calculated.
Empirical formula: The simplest whole-number ratio of atoms in a compound.

3.6: Stoichiometric Calculations

Stoichiometric calculations involve using the balanced chemical equation to determine the amounts of reactants and products in a chemical reaction.
Coefficients in a balanced equation indicate the mole ratio between reactants and products.

3.7: Limiting Reactants

Limiting reactant: The reactant that is completely consumed first in a chemical reaction and limits the amount of product that can be formed.
Excess reactant: The reactant that remains after the limiting reactant is completely consumed.

Theoretical Yield

The maximum amount of product that can be produced from a given amount of reactants.
Theoretical yield is based on the stoichiometry of the reaction.

Percent Yield

Percent Yield = (Actual Yield / Theoretical Yield) x 100
The actual yield is the experimentally measured amount of product.

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Description

This quiz covers key concepts of stoichiometry, including calculations with chemical formulas, the Law of Conservation of Mass, and the components of chemical equations. Understand how reactants and products relate and learn about the roles of subscripts and coefficients in balancing equations.