General Chemistry: Balancing Equations, Reaction Types, and Formula Calculations

Q1a. Balance the following chemical equation:

Pb(NO3)2(s) + ——> PbO(s) + NO2(g) + O2(g)

Background

Topic: Balancing Chemical Equations

This question tests your ability to balance chemical equations, ensuring the same number of each type of atom appears on both sides of the equation.

Key Terms and Concepts:

• Balancing: Adjusting coefficients so that the number of atoms of each element is equal on both sides.

• Chemical Equation: A symbolic representation of a chemical reaction.

Step-by-Step Guidance

1. List the number of atoms of each element on both sides of the equation.

2. Start by balancing the element that appears in the fewest compounds (often metals or complex ions).

3. Balance polyatomic ions as a unit if they appear unchanged on both sides.

4. Adjust coefficients as needed to balance each element, one at a time.

5. Check your work by counting all atoms again on both sides.

Try solving on your own before revealing the answer!

Q1b. Balance the following chemical equation:

C5H12(g) + O2(g) → CO2(g) + H2O(l)

Background

Topic: Balancing Combustion Reactions

This question involves balancing a hydrocarbon combustion reaction, which produces carbon dioxide and water.

Key Terms and Concepts:

• Combustion Reaction: A reaction where a hydrocarbon reacts with oxygen to form CO2 and H2O.

• Balancing: Ensuring the same number of each atom on both sides.

Step-by-Step Guidance

1. Count the number of C, H, and O atoms on both sides.

2. Balance carbon atoms first by adjusting the coefficient of CO2.

3. Balance hydrogen atoms by adjusting the coefficient of H2O.

4. Balance oxygen atoms last by adjusting the coefficient of O2.

5. Double-check all atom counts to ensure the equation is balanced.

Try solving on your own before revealing the answer!

Q1c. Balance the following chemical equation:

Al(s) + O2(g) → Al2O3(s)

Background

Topic: Balancing Synthesis Reactions

This question tests your ability to balance a synthesis reaction, where two elements combine to form a compound.

Key Terms and Concepts:

• Synthesis Reaction: Two or more reactants combine to form a single product.

• Balancing: Adjusting coefficients to ensure atom conservation.

Step-by-Step Guidance

1. Count the number of Al and O atoms on both sides.

2. Balance Al atoms by adjusting the coefficient of Al on the reactant side.

3. Balance O atoms by adjusting the coefficient of O2 on the reactant side.

4. Repeat as needed until both elements are balanced.

Try solving on your own before revealing the answer!

Q2. Identify the reaction type for each of the three reactions in question 1.

Background

Topic: Types of Chemical Reactions

This question tests your understanding of different reaction types, such as synthesis, decomposition, combustion, and single/double displacement.

Key Terms:

• Synthesis: Two or more substances combine to form one product.

• Decomposition: A single compound breaks down into two or more products.

• Combustion: A substance reacts with oxygen, releasing energy, usually producing CO2 and H2O.

• Single/Double Displacement: Atoms or ions are exchanged between compounds.

Step-by-Step Guidance

1. Examine the reactants and products for each equation.

2. Determine if the reaction involves combination, breakdown, or exchange of components.

3. Match the reaction to the appropriate type based on the patterns above.

Try classifying each reaction before checking the answer!

Q3. Calculate the formula weight of strontium phosphate, Sr3(PO4)2.

Background

Topic: Formula (Molar) Mass Calculation

This question tests your ability to calculate the formula weight (molar mass) of an ionic compound by summing the atomic masses of all atoms in the formula.

Key Terms and Formula:

• Formula Weight (Molar Mass): The sum of the atomic masses of all atoms in a chemical formula, usually in g/mol.

$\text{Formula weight} = \sum (\text{number of atoms of each element} \times \text{atomic mass of that element})$

Step-by-Step Guidance

1. Write out the chemical formula and count the number of each type of atom: Sr, P, and O.

2. Look up the atomic masses for Sr, P, and O on the periodic table.

3. Multiply the number of each atom by its atomic mass.

4. Add up all the contributions to get the total formula weight.

Try calculating before revealing the answer!

Q4. What is the percent by mass of the elements in Ag2O?

Background

Topic: Percent Composition by Mass

This question tests your ability to determine the percent by mass of each element in a compound.

Key Terms and Formula:

• Percent by Mass: The mass of a specific element in one mole of compound divided by the total molar mass, multiplied by 100%.

$\text{Percent by mass} = \frac{\text{mass of element in 1 mol compound}}{\text{molar mass of compound}} \times 100\%$

Step-by-Step Guidance

1. Determine the number of atoms of each element in Ag2O.

2. Find the atomic masses of Ag and O.

3. Calculate the total mass contributed by each element in one mole of Ag2O.

4. Calculate the molar mass of Ag2O.

5. Set up the percent by mass formula for each element, but stop before calculating the final percentages.

Try setting up the calculations before checking the answer!

Q5. Determine the empirical formula of C6H8O4N2.

Background

Topic: Empirical Formula Determination

This question tests your ability to find the simplest whole-number ratio of atoms in a compound.

Key Terms and Formula:

• Empirical Formula: The simplest whole-number ratio of elements in a compound.

Step-by-Step Guidance

1. Write the subscripts for each element: C = 6, H = 8, O = 4, N = 2.

2. Find the greatest common factor for the subscripts.

3. Divide each subscript by this factor to get the simplest ratio.

Try simplifying the subscripts before checking the answer!

Q6. A compound with the empirical formula C2H5ON has a molar mass of 118 g/mol. What is the molecular formula?

Background

Topic: Molecular Formula Determination

This question tests your ability to determine the molecular formula from the empirical formula and the compound's molar mass.

Key Terms and Formula:

• Empirical Formula: Simplest ratio of elements.

• Molecular Formula: Actual number of atoms of each element in a molecule.

$\text{n} = \frac{\text{Molar mass of compound}}{\text{Empirical formula mass}}$

Step-by-Step Guidance

1. Calculate the empirical formula mass of C2H5ON by adding the atomic masses of all atoms in the formula.

2. Divide the given molar mass (118 g/mol) by the empirical formula mass to find n.

3. Multiply each subscript in the empirical formula by n to get the molecular formula.

Try working through the steps before checking the answer!

Q7. Determine the empirical formula of the compound produced from 2.00 g sulfur and 7.13 g fluorine.

Background

Topic: Empirical Formula from Mass Data

This question tests your ability to determine the empirical formula from the masses of elements that react to form a compound.

Key Terms and Formula:

• Empirical Formula: Simplest whole-number ratio of atoms in a compound.

Step-by-Step Guidance

1. Convert the mass of each element to moles using their atomic masses.

2. Write the mole ratio of S to F.

3. Divide both mole values by the smaller number of moles to get the simplest ratio.

4. If necessary, multiply both numbers by a small integer to get whole numbers.

Try setting up the mole ratios before checking the answer!