# Chemistry Equations

• Created by: rosieruk
• Created on: 22-05-17 17:58
• Chemistry Equations
• Topic 1- atomic structure and the periodic table
• Relative atomic mass (Ar) =sum of (isotope abundance x isotope mass number) divided by sum of abundances of all isotopes
• Example: Copper has 2 stable isotopes. Cu-63 has an abundance of 69.2% and Cu-65 has an abundance of 30.8%. Calculate the Ar of copper to 1 decimal place.
• Answer: (69.2 x 63)+(30.8 x 65)/ 69.2+30.8 = 63.616= 63.6
• Topic 2- bonding, structure and properties of matter
• surface area to volume ratio = surface area divided by volume
• Topic 3- quantitative chemistry
• % mass of an element in a compound= (Ar x no of atoms of that element divided by Mr of the compound) x 100
• Example: Find the percentage mass of sodium carbonate.
• Ar of sodium= 23, Ar of carbon= 12, Ar of oxygen= 16, Mr of sodium carbonate= (2x23)+12+(3x16)= 106, 23x2 / 106 x 100= 43%
• Number of moles= mass in grams divided by Mr
• Example: How many moles are there in 66g of CO2?
• Mr= 12+(16 x 2)= 44, 66/44= 1.5 moles
• Example: 8.1g of zinc oxide reacts completely with 0.60g of carbon to form 2.2g of carbon dioxide and 6.5g of zinc. Write a balanced sybol equation for this.
• Work out Mr's ZnO: 65 + 16= 81, C: 12, CO2: 12+ (2 x 16)= 44, Zn: 65, work out how many moles for each substance: ZnO: 8.1/81= 0.1 moles, C: 0.60/12=0.050 moles, CO2: 2.2/44= 0.050 moles, Zn: 6.5/65= 0.1 moles, divide by smallest no of moles which is 0.050 moles ZnO: 0.1/0.050 = 2.0 etc C=1.0, CO2= 1.0, Zn= 2.0,Write out equation: 2ZnO + C - CO2 + 2Zn
• Example: Calculate the mass of aluminium oxide formed when 135g of aluminium is burned in the air.
• 4Al + 3O2 - 2Al2O3, Al=27, Al2O3: (2 x 27) + (3 x 16) =102, 135/27= 5, 4 moles of Al react to produce 2 moles of Al2O3- half the number of moles are produced. So, 5 moles of Al will react to produce 2.5 moles of Al2O3. mass= moles x Mr=2.5 x102= 255g
• Volume of gas= (Mass of gas/ Mr of gas) x 24
• What's the volume of 319.5g of chlorine at room temp?
• 319.5/71 x 24
• How much CO2 is formed when 30 dm3 of oxygen reacts with carbon monoxide? 2CO(g) + O2(g) - 2CO2(g)
• 1 mole of O2= 2 moles of CO2, so 1 volume of O2= 2 volumes of CO2. So 30 dm3 of O2 = (2x30 dm3)=60dm3 of CO2
• ONE MOLE OF ANY GAS OCCUPIES 24 DM3 AT 20'C
• concentration=mass of solvent/volume of solvent
• What's the concentration in g/dm3 of a solution of sodium chloride where 30g of sodium chloride is dissolved in 0.2 dm3 of water?
• 30/0.2= 150 g/dm3
• What's the concentration in mol/dm3, of a solution with 2 moles of salt in 500 cm3?
• Convert the volume to dm3 by dividing by 1000: 500 cm3/1000= 0.5 dm3. Now you've got the number of moles and the volume in the right units, just substitute them into the formula: 2/0.5= 4 mol/dm3
• concentration= number of moles of solute/volume of solvent
• mol/dm3 to g/dm3= find the concentration in mol/dm3 then use the equation: mass= moles x Mr.
• What's the concentration, in g/dm3, of 0.41666.. mol/dm3 of sulfuric acid?
• 1) Work out the Ar of the acid= H2SO4= (2x1) + 32 + (4x16) = 98  2) Convert the conceentration in moles (0.041666..) into concentration in grams: 0.041666..x98 = 4.08333.. g so, concentration= 4.08 g/dm3
• atom economy= Ar of desired products/Ar of all reactants x 100
• percentage yield= mass of product made (g)/ max theoratical mass of product x 100
• Topic 6- the rate and extent of chemical change
• Rate of Reaction= Amount of reactant used or amount of product formed/ time
• Mean rate of reaction= change in y/ change is x
• A graph shows the volume of gas released by a reaction, measured at rregular intervals. Find the mean rate of reaction between 20x and 40s
• (20s=15cm3 gas released, 40s =19cm3 gas released),  (19cm3-15cm3) / 20s =0.2 cm3/s
• Topic 8-  chemical analysis
• Rf= distance travelled by substance (B=distance from the baaseline to the centre of the spot) / distance travelled by solvent (A)