# Stoichiometry Problems in Chemistry

Stoichiometry problems in chemistry and how to solve them by the CHEMIX School program

Stoichiometry is about calculation of the quantities/relationship of/between reactants and products in a chemical reaction. It is about calculations of moles, masses and  percents within a chemical equation.

Stoichiometry problem/example No.1

A piece of metallic iron (10moles) was dissolved in conc HCl. The reaction formed H2 and FeCl2.

a) Balance: Fe+HCl>FeCl2+H2

and determine

b) amount of formed FeCl2

b) amount of used HCl

The solution

a)     Fe + 2HCl = FeCl2+H2

b)    As we can see from the balanced equation (a)  n(Fe) = n(FeCl2)  , 10 moles of FeCl2 was formed in the reaction

c) The balanced equation (a) tells us that n(HCl) = 2n(Fe) --> 20 moles of HCl was used.

The CHEMIX School Stoichiometry Problem solution

Start CHEMIX School and select push button Balance

Insert  10mFe + HCl > FeCl2 + H2  in the unbalanced equation text field and press push button Calculate Stoichiometry example/problem No.2

In following unbalanced reaction 10 grams pentane was burning:   C5H12 + O2 --> CO2 + H2O

a) Balance    C5H12 + O2 --> CO2 + H2O

b) How many grams of oxygen was used ?

c) How many grams of water was formed ?

The solution

a)  C5H12 + 8O2 = 5CO2 + 6H2O

b) 10 grams of pentane = 0.1386 moles   n(O2) = 8n(C5H12)

8 times this amount (0.1386 moles C5H12) of oxygen was used --> 8*0.1386mole*32g/mole = 35.48grams O2

c) From (a) we know that 6 times more moles of water was formed than used pentane (0.1386 moles)

n(H2O) = 6n(C5H12)      -->   6*0.1386mole*18g/mole = 14.98 grams of water

The CHEMIX School Stoichiometry Problem solution

Start CHEMIX School and select push button Balance

Insert  10gC5H12 + O2 > CO2 + H2O   in the unbalanced equation text field and press push button Calculate