CHEM 1030 EXAM THREE FORBES BOARD
EXAMINATION 2026 QUESTIONS
SOLUTIONS GRADED A+
⩥ stoichiometric coefficient. Answer: tells us the ratio of each element
in a chemical equation - based on moles
⩥ What reacts in a chemical equation?. Answer: MOLES REACT
WITH MOLES - grams do not react with grams
⩥ deriving empirical formulas from percent composition. Answer: 1.
assume you have 100 g of sample
2. convert percentages to mass values
3. convert mass to moles
4. calculate a mole ratio by dividing by the smaller mole value
5. convert mole ratio to small whole numbers
⩥ percent composition. Answer: the percentage by mass of the
constituent elements of a compound with respect to its total mass
⩥ finding percent composition. Answer: % comp.= [(mass of
element)/(total mass)] x 100
, ⩥ relationship between molecular and empirical formula. Answer:
molecular formula = (empirical formula)n
⩥ how to find n in reference to deriving molecular formula. Answer: n =
molecular mass / mass of 1 empirical formula unit
⩥ combination reaction. Answer: two or more reactants combine to form
a new larger product
⩥ decomposition reaction. Answer: a single reactant breaks down to
form 2 or more products
⩥ single displacement reaction. Answer: a single element displaces a
similar element in another compound
⩥ double displacement reaction. Answer: two elements are displaced
(like switching partners) - similar things replace similar things
⩥ combustion reaction. Answer: a rapid reaction between a
molecule/compound and oxygen that produces energy (heat)
⩥ hydrocarbon combustion. Answer: when a hydrocarbon reacts with
oxygen to form carbon dioxide and water
CH + O2 -> CO2 + H2O + heat
EXAMINATION 2026 QUESTIONS
SOLUTIONS GRADED A+
⩥ stoichiometric coefficient. Answer: tells us the ratio of each element
in a chemical equation - based on moles
⩥ What reacts in a chemical equation?. Answer: MOLES REACT
WITH MOLES - grams do not react with grams
⩥ deriving empirical formulas from percent composition. Answer: 1.
assume you have 100 g of sample
2. convert percentages to mass values
3. convert mass to moles
4. calculate a mole ratio by dividing by the smaller mole value
5. convert mole ratio to small whole numbers
⩥ percent composition. Answer: the percentage by mass of the
constituent elements of a compound with respect to its total mass
⩥ finding percent composition. Answer: % comp.= [(mass of
element)/(total mass)] x 100
, ⩥ relationship between molecular and empirical formula. Answer:
molecular formula = (empirical formula)n
⩥ how to find n in reference to deriving molecular formula. Answer: n =
molecular mass / mass of 1 empirical formula unit
⩥ combination reaction. Answer: two or more reactants combine to form
a new larger product
⩥ decomposition reaction. Answer: a single reactant breaks down to
form 2 or more products
⩥ single displacement reaction. Answer: a single element displaces a
similar element in another compound
⩥ double displacement reaction. Answer: two elements are displaced
(like switching partners) - similar things replace similar things
⩥ combustion reaction. Answer: a rapid reaction between a
molecule/compound and oxygen that produces energy (heat)
⩥ hydrocarbon combustion. Answer: when a hydrocarbon reacts with
oxygen to form carbon dioxide and water
CH + O2 -> CO2 + H2O + heat
