Stoichiometry Flashcards
1 mole =
6.023 x 10ˆ23 atoms
Molar mass
Mass of one mole of atoms; measured in gmolˆ-1
Formula for moles
n = m/M
Does conservation of moles and mass occur?
yes
Limiting reactant/reagent
When one reactant runs out before the other, and the reaction will stop. Other reactant said to be in excess
What limits the amount of products produced and the ratio of moles?
Limiting reagent
Concentration of a solution
amount of solute dissolved per volume of a solvent (mol Lˆ-1)
Concentration formula
c = n/V
Which equation helped to make fertilisers for plants and hence increase the population?
N2 + 3H2 –> 2NH3
Haber reaction
What is a solution?
Homogenous mixture of two or more substances
What is an electrolyte?
Substances whose aqueous solutions produce ions. Most likely a ionic compound. Few molecular substances solvate eg ACIDS
What is a non-electrolyte?
Substances whose aqueous solutions don’t have ions. Most likely a molecular compound.
Dissociation
In water, the elctronegative dipoles seperate ions of ionic compounds –> Solvated
Solvation stablises ions in sol, prevents ions from recombining and ions are free to move so they disperse uniformly
Strong/weak electrolytes
Strong completely dissociate but weak doesn’t it, some remain as molecules.
Solubility doesn’t say how dissociative. Some can be highly soluble but take time to dissociate and vice versa.
Chem equilibrium
determines relative no. of ions and neutral particles and they are constant
Stoichiometry
Concerned with the relative amounts of ps and rs, comes from the greek words “element” and “o measure”
How to solve a stoichiometry question?
Mass –> moles –> moles after changes in ratio –> mass
How to find the moles of individual elements in a compound?
If product is given, use their numbers eg CH4N2O
- 1 mol of C
- 4 mols of H
- 2 moles of 2
- 1 mol of O
To start the equation…
solve for sum of reactants = sum of products and that the eqs are balanced
Another word for c
Molarity or M
Going from reactant mols –> product mols
Adjust to the ratio, other way then follow the ratio
How to find the LR
Compare to set eq using the moles provided in question. To find product moles, use the limiting reactant.
Excess reactant?
Find how much of the limiting reactant’s moles were used. Same amount of excess will be used. ER - LR = excess amount
To find moles between reactants?
Set ratio, 1:1 or use percentage method i.e compare moles to set eq and see how much percentage reduction it was
