Introducing chemical reactions

• What is the task in C3.1a?

  Use chemical symbols to write formulae
• How do you balance the charges of ions in simple ionic compounds?

  Balance the charges of the ions involved
• What is the method to balance simple covalent compounds?

  Imagine the ion and balance the charges
• What is the principle used in C3.1b to write formulae and balanced chemical equations?

  Principle of conservation of mass
• How do you write a balanced chemical equation?

  Count the number of atoms on both sides
• What is the purpose of using large numbers in balancing chemical equations?

  To balance the equation so that there is the same amount of each element on each side
• How do ions form in a compound?

  Atoms form ions to have a stable arrangement of electrons
• What is the charge of ions from group 1 elements?

  1+
• What is the charge of ions from group 7 elements?


  1-
• How do you construct a balanced ionic equation?

  Write out the full chemical equation, split (aq) substances into ions, cancel out spectator ions
• What does the state symbol (s) represent?

  Solid
• What is the definition of the Avogadro constant?

  6.02 x 10^23 per mole
• How is the mass of a substance related to the amount of that substance in moles?

  The mass of one mole of a substance is numerically equal to its relative formula mass
• How do you convert between moles and grams of a substance?

  Using the formula: Moles = Mass / Mr
• What are the common ions and their charges?

  Group 1: 1+, Group 2: 2+, Group 3: 3+

  Group 5: 3-, Group 6: 2-, Group 7: 1-

  NO3- (nitric acid), Cl- (hydrochloric acid), SO42- (sulfuric acid)
• What is the principle of conservation of mass?

  The total mass of the reactants is equal to the total mass of the products
• How do you calculate the number of moles of a substance?

  Using the formula: Moles = Mass / Mr
• What is the definition of a mole?

  Amount of substance
• What is the difference between a mole and a molecule?

  A mole is a unit of amount of substance, while a molecule is a group of atoms
• What is the concept of spectator ions?

  Ions that are not involved in the reaction and cancel out
• What is the concept of limiting reactants?

  The reactant that is used up and limits the amount of products
• Why is it important to balance chemical equations?

  To ensure that the number of atoms of each element is the same on both sides of the equation
• What is the purpose of using state symbols in chemical equations?

  To represent the physical state of the substances
• What is the relationship between the number of particles in one mole of a substance and the number of particles in one mole of any other substance?

  They are the same
• What is the formula to convert between moles and grams?

  Moles = Mass / Mr
• What is the term for the reactant that is used up and limits the amount of products?

  Limiting reactant
• What happens to the amount of excess reactant when a limiting reagent is used?

  It is limited to the amount that reacts with the limiting reagent
• How do you use a balanced equation to calculate masses of reactants or products?

  1. Find moles of the substance you’re given the mass of: moles = mass / molar mass
  2. Use balancing numbers to find the moles of desired reactant or product
  3. Mass = moles x molar mass (of the reactant/product)
• What is the law of conservation of mass?

  No atoms are lost or made during a chemical reaction
• What is the relationship between the mass of the products and the mass of the reactants in a chemical reaction?

  They are equal
• How do you explain observed changes in mass in non-enclosed systems during a chemical reaction using the particle model?

  1. Check if the change in mass is due to a reactant or product as a gas
  2. Consider the mass of the gas that has not been taken into account
• How do you deduce the stoichiometry of an equation from the masses of reactants and products?

  1. Convert the masses in grams to amounts in moles (moles = mass/Mr)
  2. Convert the numbers of moles to simple whole number ratios
  3. Use the ratios to deduce the stoichiometry of the equation
• What is the balanced equation for the reaction between Cu and O2 to form CuO, given the masses of reactants and products?

  2Cu + O2 -> 2CuO
• What is the term for the study of the balancing numbers in front of compounds/elements in reaction equations?

  Stoichiometry
• Why is it important to use the moles/mass of the limiting reagent for calculations?

  Because it limits the amount of products formed