chemical maths! Flashcards
what is a mole?
the relative atomic mass (Ar) of an element in grams (or the relative formula mass (Mr) in grams if it’s a compound)
what is Avogadro constant?
The number of particles in one mole of particles, 6.02 × 10²³ per mole.
equation for the number of particles:
Number of particles = 6.02 × 10^23 × mol
equation for calculating mass of a susbtance:
mass (g) = mr x moles
when does a reaction finish?
when one of the reactants is all used up
how could be differentiate between the limiting reactant and the excess? (2)
- reactant that is all used up is = the limiting reactant
- reactant that is left over = in excess
what does the mass of product formed in a reaction depend on? why?
- the mass of the limiting reactant.
- because no more product can form when the limiting reactant is all used up.
The maximum mass of product formed in a reaction can be calculated using: (3)
- the balanced equation
- the mass of the limiting reactant, and
- the Ar or Mr values of the limiting reactant and the product
define ‘stoichiometry/ empirical formula’
the ratio of the amounts of each substance in the balanced equation
how can stoichiometry/ empirical formula be calculated?
GRAMS/RAMS (grams over rams) and then divide by the smallest value
What does the law of conservation of mass state? (2)
- mass is always conserved in a chemical reaction
- no atoms are lost or made during a chemical reaction
Why is it more difficult to measure the mass of a gas than the mass of a liquid or solid?
A gas can easily escape into the air
A chemical reaction is carried out in a beaker on a balance.
Why may the balance reading for the products be less than the reading for the reactants?
- Some of the reactants may have been spilled
- One of the products was a gas and floated off
Why may the balance reading for the products be more than the reading for the reactants?
Gas from the air reacted with the reactants
concentration equation:
concentration (g/dm^3) = mass (g) / volume (dm^3)
