3.2.3 Using balanced equations to calculate reacting masses

• Why is it important to have the same number of atoms for each element in a balanced equation?

  To obey the law of conservation of mass
• What does a balanced chemical equation show?

  The exact number of each atom
• What are the steps to balance a chemical equation?

  1. Write the chemical formula for each reactant and product.
  2. Count the number of atoms for each element on both sides.
  3. Use coefficients to adjust amounts until balanced.
• In the equation H2 + O2 → H2O, what does it mean when it is balanced as 2H2 + O2 → 2H2O?

  Two hydrogen molecules react with one oxygen molecule
• What are coefficients in a chemical equation?

  Numbers in front of chemical formulas
• How does the balanced equation 2H2 + O2 → 2H2O illustrate the conservation of mass?

  Atoms are conserved; same number on both sides
• In the equation with hydrogen and oxygen, what is the product formed?

  Water (H₂O)
• How do hydrogen and oxygen relate in a chemical reaction?

  They react together to create water
• What is the definition of molar mass?

  Mass of one mole of a substance
• In what units is molar mass measured?

  Grams per mole (g/mol)
• How do you calculate the molar mass of water (H₂O)?

  2(1.01) + 16.00
• What are the steps to find the molar mass of a substance?

  1. Look up atomic masses from the periodic table.
  2. Add atomic masses for each element in the compound's formula.
• What is the molar mass of water (H₂O)?

  18.02 g/mol
• What is the molar mass of carbon dioxide (CO₂)?

  44.01 g/mol
• How do you calculate the molar mass of carbon dioxide (CO₂)?

  12.01 + 2(16.00)
• What should you remember about significant figures in molar mass calculations?

  • Use the correct number of significant figures.
  • Ensure accuracy in the final result.
• What is the formula to convert mass to moles?

  Moles = Mass / Molar Mass
• What is the process to convert grams of a substance to moles?

  Divide mass by molar mass
• How many moles are in 50 grams of Carbon Dioxide (CO₂)?

  1.14 moles
• What is the relationship between moles of hydrogen and moles of oxygen in the reaction $2H_{2} +$$O_{2} \rightarrow 2H_{2}O$?


  2 moles of hydrogen react with 1 mole of oxygen
• If you have 3 moles of water, what is the molar mass of water used in the calculation?

  Approximately 18 g/mol
• What is the symbol for mass in chemistry?


  m
• What are the key terms and their symbols related to moles, mass, and molar mass?

  • Moles: n
  • Mass: m
  • Molar Mass: M
• What does the calculation of 3 moles of water yield in grams?

  It yields a mass of 54 grams
• If 4 moles of hydrogen react, how many moles of oxygen are needed?

  2 moles of oxygen
• How do you calculate the mass of 3 moles of water?

  Mass = 3 moles × 18 g/mol
• What is the mass of 3 moles of water calculated using the formula?

  54 g
• What does the mass ratio indicate in a chemical reaction?

  It shows how much of each substance is needed
• What are the formulas related to moles, mass, and molar mass?

  1. Moles = Mass / Molar Mass
  2. Mass = Moles × Molar Mass
  3. Molar Mass = Mass / Moles
• How do you find the mass ratio in a chemical reaction?

  1. Get the balanced equation
  2. Determine molar masses
  3. Multiply molar masses by coefficients
• What is the basis for the mass ratio in a chemical reaction?

  It is based on molar masses and coefficients
• What is the balanced equation for the reaction of hydrogen and oxygen to form water?

  $2H_{2} +$$O_{2} \rightarrow 2H_{2}O$
• What is the molar mass of $H_{2}$?


  2.02 g/mol
• How much $O_{2}$ is needed to produce 36.04 g of water?


  32.00 g
• What are the calculated masses of substances in the reaction?

  • <latex>H_{2}</text{: 4.04 g}
  • <latex>O_{2}</text{: 32.00 g}
  • <latex>H_{2}O</text{: 36.04 g}
• How is $1.23 \times 10^{5}$ rounded to 2 significant figures?


  $1.2 \times 10^{5}$
• Why is it important to keep the correct number of significant figures?

  It ensures calculations are accurate and precise
• What is the significance of balancing chemical equations in chemistry?

  • Ensures conservation of mass
  • Reflects accurate stoichiometry
  • Predicts amounts of products formed
• What symbol represents mass in the formula?


  m
• What are reactants in a chemical reaction?

  Substances that start a chemical reaction