Stoichiometry & Moles – Lecture Review

18 question-and-answer flashcards summarising key definitions, formulas, and calculations related to moles, stoichiometry, gas laws, empirical formula, percentage yield, atom economy, and limiting reagents.

What is a mole?

The amount of substance that contains the same number of particles as there are atoms in 12 g of carbon-12 (Avogadro’s constant, 6.022 × 10²³ mol⁻¹).

What is Avogadro’s constant?

6.022 × 10²³ mol⁻¹—the number of particles in one mole of any substance.

How do you calculate the number of moles from particles?

Moles = Number of particles ÷ Avogadro’s constant.

How do you calculate the number of moles from mass?

Moles = Mass (g) ÷ Molar mass (g mol⁻¹).

How do you calculate mass from number of moles?

Mass = Moles × Molar mass.

What is molar mass?

The mass of one mole of a substance, numerically equal to its relative atomic or molecular mass in g mol⁻¹.

How do you calculate the number of moles of a gas at RTP?

Moles = Volume (dm³) ÷ 24.0.

What does RTP stand for and what are its conditions?

Room Temperature and Pressure: 20 °C (293 K) and 101 kPa; one mole of gas occupies 24.0 dm³.

How do you convert between cm³ and dm³?

1 dm³ = 1000 cm³.

What is the ideal gas equation?

pV = nRT, where p = pressure (Pa), V = volume (m³), n = moles, R = 8.31 J mol⁻¹ K⁻¹, T = temperature (K).

How do you convert °C to K?

K = °C + 273.

What is the empirical formula?

The simplest whole-number ratio of atoms in a compound.

What is the molecular formula?

The actual number of atoms of each element present in one molecule of a compound.

How do you calculate an empirical formula from masses or percentages?

1) Divide each element’s mass or % by its Ar; 2) Divide all results by the smallest value; 3) Convert to the simplest whole-number ratio.

What is percentage yield?

Percentage yield = (Actual yield ÷ Theoretical yield) × 100.

What is atom economy?

Atom economy = (Mass of desired product ÷ Total mass of all products) × 100.

Why are high atom economy and yield important in chemical processes?

They minimise waste, lower costs, and reduce environmental impact by using resources more efficiently.

What is a limiting reagent?

The reactant that is completely used up first in a reaction, thus limiting the amount of product that can form.