Limiting Reactants

• What is a limiting reactant?

  A reactant that gets used up first
• Why do reactions stop?

  When one reactant is completely used up
• What happens when magnesium carbonate reacts with hydrochloric acid?

  Bubbles of gas are produced
• What indicates that a reaction is taking place?

  Visible bubbles of gas being released
• What is the effect of adding excess reactants?

  They ensure the limiting reactant is fully used
• What is the relationship between limiting reactant and product formed?

  Product amount is proportional to limiting reactant
• If you double the amount of limiting reactant, what happens to the product?

  The amount of product also doubles
• Why does adding more reactant increase product formation?

  More reactant particles lead to more product particles
• How can you calculate the mass of a product formed?

  Using the mass of the limiting reactant
• What is the first step in calculating the mass of a product?

  Write out the balanced reaction equation
• What do you need to find after writing the balanced equation?

  Relative formula masses of reactants and products
• How do you find the number of moles of a substance?

  Divide mass by molar mass
• What does the balanced equation tell you about moles?

  It shows the ratio of moles of reactants and products
• If 4 moles of Al react, how many moles of Al₂O₃ are produced?

  2 moles of Al₂O₃ are produced
• How do you calculate the mass of a product from moles?

  Mass = moles × molar mass
• What is the yield of a reaction?

  The mass of product formed
• What are theoretical yields?

  Calculated maximum mass of product
• Why is the actual yield usually less than theoretical yield?

  Because reactions rarely go to completion
• What are the steps to calculate the mass of potassium chloride produced from potassium bromide?

  1. Write the balanced equation.
  2. Calculate relative formula masses.
  3. Find moles of potassium bromide.
  4. Use the balanced equation for moles of potassium chloride.
  5. Calculate the mass of potassium chloride.
• What is the balanced equation for the reaction between chlorine and potassium bromide?

  Cl₂ + 2KBr → Br₂ + 2KCl
• What are the atomic masses of potassium, bromine, and chlorine?

  K: 39, Br: 80, Cl: 35.5