Equations

• The gas equation

  $PV =$$nRT$

  P is for pressure measured in Pa

  V is for volume measure in m³

  n is the number of moles

  R is the gas constant

  T is temperature measured in Kelvin
• Specific heat capacity

  $q =$$mc∆T$

  q is heat energy measured in joules

  m is mass of substances measured in g

  c is the specific heat capacity measured in J/g°c

  ∆T is the change is temperature measured in °c
• Moles

  $Mol =$$mass ÷ Mr$
• Concentration

  $Concentration=$$mol ÷ volume$

  Concentration is measured in moldm-³

  Mol is moles

  Volume is measured in dm-³

  Cm³ ÷ 1000 = dm³
• Atom economy

  %atom economy = molecular mass (Mr) of desired product / total molecular mass of reactants * 100%
• Atom economy shows how many atoms from the reactants are found in useful products and how many are wasted.

  You can improve atom economy by changing a reaction to have fewer waste products or by finding a use for the waste
• Percentage yield of a chemical reaction is about the efficiency of the reaction.

  Efficiency can be affected by the reaction being reversible or not being complete or side reactions happening
• Equilibrium constant ( Kc)

  aA + bB ⇌ cC + dD

  Kc = [C]^c × [D]^d ÷ [A]^a × [B]^b

  So it's the concentration of the substance to the power of the balancing numbers measured in moldm^-3
• Enthalpy change equation

  -q÷n

  q is heat energy measure in J

  n is the number of moles
• Mean enthalpy change

  Sum of enthalpy of reactants - sum of enthalpy of products
• Kinetic energy

  KE = 1/2 × mass × v²

  Mass in kg

  KE in joules
• Energy of reaction

  q = mass × specific heat capacity × ∆T

  Mass in g

  T is temperature measured in °C
• Enthalpy of combustion

  It's the enthalpy change where one mole of a substance is completely burned in excess oxygen in standard conditions with all reactants and products in standard state
• Enthalpy of formation

  It's the enthalpy change where one mole of a compound is formed from its constituent elements under standard conditions and with all reactants and products in standard state
• Enthalpy of combustion

  Enthalpy of combustion = enthalpy of reactants - enthalpy of products
• Enthalpy of formation

  Enthalpy of formation = products - reactants
• Volume of gas at room temperature

  24 × moles
• Percentage yield

  Percentage yield = Actual yield / theoretical yield * 100% using moles
• Relative atomic mass


  ( Mr of abundance 1) + ( Mr of abundance 2 ) + ( Mr of abundance 3) / total abundance
• Relative atomic mass

  It's the average mass of 1 atom of an element compared to 1/12 of an atom of 12C
• Arrhenius equation

  K = Ae^(EA/RT)

  K is the rate constant ( units vary per reaction )

  A is the A constant ( units same as k)

  e is exponential button on the calculator

  EA is the activation energy ( units is Jmol-¹ )

  R is the gas constant

  T is temperature measured in Kelvin
• Arrhenius equation pt2

  • As EA becomes larger then k becomes slower so a large EA means a slower rate
  • If you increase T ( temperature) then k will increase so a larger t means a faster rate
• Arrhenius equation pt3

  Logging both sides would make the equation look like

  ln(k) = ln(A) - EA/RT

  Y = c+ mx

  This allows you to draw a graph with ln(k) being y , ln(A) being c and -EA/RT being mx . Gradient = -EA/R
• Calculating empirical formula

  E.g. A compound contains 85.7g of carbon and 14.3g of hydrogen. What is it's empirical formula?

  First work out moles

  Moles = mass/Mr

  Carbon moles = 85.7/12 =7.141

  Hydrogen moles = 14.3/1 = 14.3

  Divide moles by lowest mole

  So 7.141/7.141 and 14.3/7.141

  Would give a 1:2 ratio

  Final answer would be CH2