chem calculations

there are many calculations using the mole ; 

• number of particles = moles x Avogadro's constant (6.02x10^23)
• number of moles = mass / Mr
• number of moles = concentration (moldm^-3) x volume (dm^3)

pV = nRT 

p - pressure (pa)

V - volume (m^3)

n - moles 

R - gas constant (8.31 jk^-1mol^-1)

T - temperature (k - +273 degrees)

• 1 - write out balanced equation 
• 2- find the Mr of given compound 
• 3- from the given mass, find moles by mass/Mr
• 4- use the ratios in the equation and the calculated moles to find the moles of the required compound
• 5- find the Mr of the require compound
• 6- use the Mr and moles to find the mass by mol / Mr

• 1 - match each element to it's % and find its Mr
• 2- find the moles of each element by % / Mr
• 3 - divide each of the moles by the smallest number of moles you have calculated
• 4- this is the ratio of elements, use this to write the formula

• 1- find the moles of each element by mass / Mr 
• 2- find the ratio of moles by dividing all the mol values by the smallest mol value you have calculated.
• 3- use this to write your emprical formula. 

• 1- write a balanced equation for the compounds you need 
• 2 - work out the moles of the compound given using conc. x vol. 
• 3- use the mole ratios from the equation to work out the moles of the required compound
• 4- use conc. = mol / vol to find concentration. 

• 1 - find the theoretical yield by: 
  • a - use mass / Mr to find moles of the given product
  • b - use mole ratios from the balanced equation to find moles of required compound
  • c - find  the mass by moles x Mr 
• 2 - substitute this into this equation: 
  • % yield = actual yield / theoretical yield
  • you will be given the actual yield 

% atom economy = Mr of desired product / sum of Mrs of all reactants x 100 

• 1 - find the bonds broken, use the balanced equation. add their mean bond enthalpy values. 
• 2- do the same for bonds made 
• 3- minus the value for bonds made from the value of bonds broken to give total change.
  • enthalpy change  = total energy absorbed - total energy released.