← Chemistry syllabus

VirginiaChemistry

Molar Relationships and Chemical Reactions

6 dot points across 6 inquiry questions. Click any dot point for a focused answer with worked past exam questions where available.

Why must a chemical equation be balanced, and how do you balance one?

Balancing equations and conservation of mass: balance chemical equations by adjusting coefficients to satisfy the law of conservation of mass.
A focused Virginia SOL Chemistry answer on chemical equations under CH.3: the law of conservation of mass, why only coefficients (not subscripts) may change, and a reliable method for balancing equations including combustion.
9 min answer →

Which reactant runs out first, and how much product do you really get?

Limiting reactants and percent yield: identify the limiting and excess reactants, calculate the theoretical yield, and calculate the percent yield.
A focused Virginia SOL Chemistry answer on yield under CH.3: identifying the limiting and excess reactants, calculating the theoretical yield of product from the limiting reactant, and finding the percent yield from the actual yield.
9 min answer →

How do you find what fraction of a compound is each element, and its simplest formula?

Percent composition and empirical formulas: calculate the percent composition by mass of a compound and determine its empirical and molecular formulas from composition data.
A focused Virginia SOL Chemistry answer on composition under CH.3: calculating percent composition by mass from a formula, finding the empirical formula from percent data, and scaling the empirical formula to the molecular formula using the molar mass.
9 min answer →

How does a balanced equation let you calculate the amount of product from the amount of reactant?

Stoichiometry and the mole ratio: use the mole ratio from a balanced equation to convert between moles and masses of reactants and products, including gas volumes at STP.
A focused Virginia SOL Chemistry answer on stoichiometry under CH.3: reading the mole ratio from a balanced equation, mole-to-mole and mass-to-mass calculations, and using the molar volume of a gas at STP, with the full three-step chain.
10 min answer →

How does the mole connect the mass of a sample to the number of particles it contains?

The mole and molar mass: use the mole, molar mass and Avogadro's number to convert between mass, moles and number of particles.
A focused Virginia SOL Chemistry answer on the mole under CH.3: Avogadro's number, finding the molar mass from the periodic table, and converting between mass, moles and number of particles, the master skill behind all chemical calculations.
9 min answer →

How do you recognize and predict the products of the five reaction types?

Types of chemical reactions: classify reactions as synthesis, decomposition, single replacement, double replacement or combustion, and predict their products.
A focused Virginia SOL Chemistry answer on reaction types under CH.3: the five categories (synthesis, decomposition, single replacement, double replacement, combustion), how to recognize each, and how to predict the products including using an activity series.
9 min answer →