Stoichiometry and Limiting Reactants
A student mixes two reactants. After the reaction is complete, one reactant is still present in the container. What must be true?
The reaction was incomplete
The remaining reactant was limiting
The remaining reactant was in excess
The equation was unbalanced
The remaining reactant was in excess
Two clear solutions are tested for conductivity. Solution A lights a bulb brightly while solution B produces a dim glow. What is the best explanation for this phenomenon?
A has more mass
A produces more ions in solution
B is hotter
B has higher density
A produces more ions in solution
Two colorless solutions are mixed and a cloudy solid forms immediately. What is the most likely explanation for this?
A gas formed
Heat was absorbed
The solution became dilute
An insoluble compound formed
An insoluble compound formed
Two different reactions produce the same net ionic equation.
What does this imply?
The reactions are identical in every way
The reactants are identical
The products are identical
The same ions undergo the same chemical change
The same ions undergo the same chemical change
Two substances absorb the same amount of heat. One increases in temperature more. What does this indicate about this substance.
Same specific heat
Higher specific heat
Lower specific heat
Same mass
Lower specific heat
Two students perform the same reaction. One calculates product using grams directly, the other converts to moles first. Their final answer differs. Why?
Grams are not conserved
Only moles follow mole ratios in equations
Chemical reactions happen based on mass and not moles
Mass is irrelevant
Only moles follow mole ratios in equations
A solid ionic compound is tested for conductivity before and after dissolving in water. They observed that the solid conducts no electricity while the solution strongly conducts electricity. Why?
Charges are created during dissolution
Ions become mobile in solution
Water provides electrons
The compound changes identity
Ions become mobile in solution
A student mixes two solutions and observes no precipitate, even though a double replacement reaction was expected. Why?
The reaction failed
All possible products are soluble in the solvent
Temperature is too low
Not enough reactants
All possible products are soluble in the solvent
A student forgets to remove spectator ions when writing a net ionic equation. What is the result?
Incorrect products
Charges are unbalanced
Equation shows unnecessary species
Reaction does not occur
Equation shows unnecessary species
A hot metal is placed in water and cools down. The water warms up. Why?
Energy is created
Heat flows from cold to hot to reach equilibrium temp
Temperature equalizes instantly
Heat flows from hot to cold to reach equilibrium temp
Heat flows from hot to cold to reach equilibrium temp
A reaction is scaled up by doubling all reactants. What happens to the theoretical yield?
Stays the same
Doubles
Halves
Cannot be determined
A student dissolves equal molar amounts of NaCl and CaCl2 in separate solutions. The CaCl2 solution conducts better electricity. Why?
CaCl2 is heavier
CaCl2 produces more ions per formula unit
NaCl is insoluble
CaCl2 reacts with water
CaCl2 produces more ions per formula unit
A compound is predicted to be insoluble based on solubility rules, but no precipitate forms in experiment. What is the BEST explanation for this?
The rules are incorrect
Not enough product was formed to see a solid precipitant
The compound dissolved anyway
The reaction reversed
Not enough product was formed to see a solid precipitant
Two experiments use the same reactants and conditions, but one has lower percent yield. What is the most likely reason?
One reaction had a more efficient reaction
They used different molar masses
Product was lost or there were side reactions
The balanced equation changed between the two reactions
Product was lost or there were side reactions
A student calculates heat and gets a negative value. What does this mean?
Heat was absorbed
Heat was released
There was no heat transfer
There was an error in calculations
Heat was released
A hydrocarbon burns in limited oxygen, producing CO instead of CO2. Why?
Incomplete combustion
Reaction was too fast
Water interferes
Too much oxygen
Incomplete combustion
A solution is diluted by adding water. The number of moles of solute stay the same. What changes?
Mass
Molarity
Identity
Charge
Molarity
A reaction produces a solid and a clear solution. The solid is removed by filtration. What type of reaction occurred?
Combustion
Precipitation
Decomposition
Acid-base
Precipitation
A student calculates a percent yield of 120%. What is the BEST conclusion?
Calculation or measurement error occurred
Limiting reactant was wrong
Reaction exceeded theoretical limits
Reaction was very efficient
Calculation or measurement error occurred
Two objects reach the same final temperature after contact. What has occurred?
Reaction completion
Energy loss
Thermal equilibrium
Phase change
Thermal equilibrium
A reaction produces less product than expected. Both reactants were completely consumed. What is the BEST explanation for this?
Limiting reactant was incorrect
Equation was unbalanced
Reaction stopped early
Side reactions reduced yield
Side reactions reduced yield
Two solutions have the same molarity, but one contains more total solute. Why?
Different temperatures
Different densities
Different volumes
Different ions
Different volumes
A student forgets to convert mL to L when calculating molarity. What happens to the answer?
Answer is too large
Answer is too small
Units cancel
No effect
Answer is too small
A larger mass of the same substance requires more heat to raise its temperature. Why?
Higher density
Higher molarity
More particles require more energy
Lower conductivity
More particles require more energy
A student identifies the reactant with the smallest mass as limiting, but gets the wrong answer. Why?
Mass determines limiting reactant
Smaller mass reacts faster
Mole ratio determines limiting reactant
Density determines limiting reactant
Mole ratio determines limiting reactant