Limiting Reactants

• What happens to reactions when one reactant is used up?

  Reactions stop
• What indicates that a reaction is taking place when magnesium carbonate is used?

  Lots of bubbles of gas are produced
• What happens to the amount of fizzing over time in a reaction?

  It slows down
• What is the limiting reactant in a chemical reaction?

  The reactant used up first
• What happens to other reactants when the limiting reactant is used up?

  They remain in excess
• How is the amount of product formed related to the limiting reactant?

  It is directly proportional to it
• If you have a certain amount of limiting reactant, how can you find the amount of product formed?

  By using the balanced reaction equation
• What is the first step to calculate the mass of a product formed?

  Write out the balanced equation
• How do you calculate relative masses of reactants and products?

  Using the balanced equation
• How can you determine the number of moles of a substance in a reaction?

  By using the balanced equation
• How do you calculate the mass of a product formed from a limiting reactant?

  Using the mass of the limiting reactant
• What should you write out to calculate the mass of aluminum oxide formed?

  The balanced equation
• What is the relationship between the limiting reactant and the amount of product formed?

  • The amount of product is directly proportional to the limiting reactant.
  • If the limiting reactant is used up, the reaction stops.
  • Other reactants remain in excess.
• What steps should you follow to calculate the mass of a product formed in a reaction?

  1. Write out the balanced equation.
  2. Calculate relative masses of reactants and products.
  3. Use the mass of the limiting reactant.
  4. Determine the number of moles of the substance.
  5. Calculate the mass of the product formed.
• How does adding more reactants affect the reaction?

  • More reactants lead to more particles.
  • This can increase the amount of product formed.
  • However, the limiting reactant will still determine the maximum product.
• What is the significance of the balanced equation in chemical reactions?

  • It shows the ratio of reactants to products.
  • It helps calculate the mass of products formed.
  • It identifies the limiting reactant.
• How many moles of product will be made from this many moles of reactant?

  2.5 moles
• What is the first step to calculate the mass using the number of moles?

  Use the number of moles to calculate mass
• How do you calculate the mass of aluminum oxide formed from 135 g of aluminum burned in air?

  Write the balanced equation for the reaction
• What is the balanced equation for the reaction of aluminum with oxygen?

  • 4Al + 3O₂ → 2Al₂O₃
• How do you calculate the relative formula masses of aluminum and aluminum oxide?

  Use the atomic masses of each element
• What is the relative formula mass of aluminum?

  27
• What is the relative formula mass of aluminum oxide?

  102
• How many moles of aluminum are in 135 g?

  5 moles
• What is the ratio of moles in the balanced equation for aluminum and aluminum oxide?

  4 moles of Al produce 2 moles of Al₂O₃
• How many moles of aluminum will react to produce 2.5 moles of aluminum oxide?

  5 moles of aluminum
• What is the mass of 2.5 moles of aluminum oxide produced?

  255 g
• What is the yield of a reaction?

  The mass of product formed in a reaction
• What is the theoretical yield in a chemical reaction?

  The maximum amount of product expected
• Why might the actual yield be less than the theoretical yield?

  Because reactions are not 100% efficient
• What is the balanced equation for the reaction between chlorine and potassium bromide?

  Cl₂ + 2KBr → Br₂ + 2KCl
• How do you calculate the mass of potassium chloride produced from 23.8 g of potassium bromide?

  Use the balanced equation and molar masses
• What are the atomic masses used in the calculations?

  A(K) = 39, A(Br) = 80, A(CI) = 35.5
• What is quantitative chemistry concerned with?

  • The calculation of reactants and products
  • The measurement of amounts in chemical reactions