Chemistry Equations You Need To Know

Question 1

How do you calculate % by mass?

Answer 1

% by mass = Mr of single element / Mr of Whole Compound x 100

Question 2

How do you calculate the number of particles or moles in a substance using Avogadro’s constant?

Answer 2

Number of particles = Moles x Avogadro’s constant (6.02 x1023)

1023 is 10 to the power of 23

OR

Moles= Number of particles/Avogadro’s constant (6.02 x 1023)

Question 3

How do you calculate Moles using mass and Mr? (1)

Answer 3

Moles = Mass (g) / Mr
N = m/Mr

Question 4

How do you calculate Moles using concentration and volume? (2)

Answer 4

Moles = conc (mol/dm3) x vol (dm3)

n = c x v

Question 5

How do you calculate Mass using concentration and volume?

Answer 5

Mass = conc (g/dm3) x vol (dm3)

m = c x v

Question 6

How do you calculate RAM (Relative Atomic Mass/Ar of isotopes)?

Answer 6

RAM= (Abundance 1 x Mass 1) + (Abundance 2 x mass 2)/100

The equation above is used when you have two isotopes of the same element, an isotope of an element is when an element has a different Ar due to having more or less neutrons.
Ar is the Relative Atomic Mass of an atom for 1 element (these are given to us on the periodic table, it’s the top number- e.g. Carbon is 12).
Mr is the Relative Formula Mass- the total Ar/mass of a compound or molecule. e.g CO2= (12x1) + (16x2) =44

Question 7

How do you calculate Percentage Yield?

Answer 7

Percentage Yield= Actual Yield/Theoretical Yield x 100

Question 8

How do you calculate Atom Economy?

Answer 8

Atom Economy= Mr of desired product/Mr of all products x 100

Question 9

How do you calculate Mr?

Answer 9

Mr=mass(g)/Moles
Mr=m/N

Question 10

How do you get from dm3 to cm3?

How do you get from cm3 to dm3?

Answer 10

Multiply the value in dm3 by 1000 to get cm3

Divide the value in cm3 by 1000 to get dm3

Question 11

How do you calculate Volume using Moles and dm3?

Answer 11

Volume = Moles x 24dm3

V = n x 24dm3

dm3 is decimetres cubed

Question 12

How do you calculate Mass using Mr and Moles?

Answer 12

Mass(g)= Mr x Moles
m= Mr x N
Remember mass equals Mr Moles

Question 13

How do you get from mol/dm3 to g/dm3?

How do you get from g/dm3 to mol/dm3?

Answer 13

Multiply the mol/dm3 value by the relative formula mass to get to g/dm3.

Divide the g/dm3 value by the relative formula mass to get to mol/dm3.

Question 14

How do you calculate Ar/Relative Atomic Mass of an atom?

Answer 14

It’s the mass of an atom, e.g. Oxygen- the Ar is 16.

Question 15

How do you calculate the rate of a reaction?

Answer 15

Amount of product formed/time
OR
Amount of reactant used up/time

Units could be cm^3/s, g/s, mol/s