Amounts of substances in equations (HT only) Flashcards – AQA GCSE Combined Science: Trilogy (8464) — Chemistry — Higher

What do coefficients in a balanced chemical equation represent in terms of amount of substance?

The fixed mole ratio in which substances react and are formed.

What is the mole ratio of magnesium, hydrochloric acid, magnesium chloride and hydrogen in $\ce{Mg + 2HCl -> MgCl2 + H2}$?

$1:2:1:1$

How are mole ratios used in chemical calculations?

They determine how much of one substance is needed or produced from a known amount of another.

What must be done to a chemical equation before using it for an amount calculation?

Balance the equation.

How can you calculate the mass of one substance from a known mass of another using a balanced equation?

1. Convert the known mass to moles using its molar mass.
2. Use the equation’s coefficient ratio to find the required moles.
3. Convert those moles to mass using the required substance’s molar mass.

How can you find the mass relationships implied by a balanced chemical equation?

Treat the coefficients as relative numbers of moles, then multiply each by its substance’s molar mass.