C4.2 - Equations And Calculations (Go back and learn calculations)

Question 1

How do you find out the number of moles of each substance involved in a chemical reaction?

Answer 1

Using the balanced symbol equation of that reaction 2H2 + O2 ->2H2O 2 mol of H2, 1 of O2

Question 2

H2 + Cl2 –> 2HCl

How many moles of H2, Cl2 and HCl are there?

Answer 2

H2 : 1 mole
Cl2 : 1 mole
HCl : 2 moles

Question 3

2Mg + O2 –> 2MgO

If you have 6g of Mg how do you calculate the g of O2 you have?

Answer 3

Step 1) g –> moles
Find how many moles of mg you have:
6g / 24 Ar = 0.25 moles

Step 2) Ratio
Find the ratio between mg to O2:
2Mg + 1O2
2:1 ratio

Step 3)ratio --> moles
Find the moles of O2
2:1 Mg:O2
0.25:0.125
0.125 moles

Step 4) moles –> g
Find the g of O2
1 mole of O2 = 16*2 = 32g

0.125 moles * 32 = 4g

4g

Question 4

How do you balance equations using reacting masses?

Answer 4

1) Divide the mass of each substance by it’s relative formula mass to find the number of moles
2) Divide the number of moles of each substance by the smallest number of moles in the reaction
3) If resulting numbers are not whole multiple till all are whole
4) Those numbers are the mol of each substance