What mass of carbon dioxide is produced from burning 100 grams of ethanol in oxygen according to this reaction: C2H5OH + 3 O2 --> 2 CO2 + 3 H2O

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When approaching a question like this I always find it easier to write out the equation with the known quantities written underneath each individual compound.  This allows us to easily check whether the equation is balanced

                                   C2H5OH          +         3 O2     -->       2 CO2                         +          3 H2O

We can see that this equation is balanced as it has 2 carbons, 6 hydrogens, and 7 oxygens on each side.

We are trying to work out the mass of CO2 and we already know what mass of ethanol (C2H5OH) we have.  We can also work out the gram formula mass of each compound we are interested in. 

gfm CO2 = (1 x 12) + (2 x 16) = 44 g/mol

gfm C2H5OH = (2 x 12) + (6 x 1) + (1 x 16) = 46 g/mol

Next we need to decide what formula we can use to figure out the mass of CO2 from the data that we have. 

                                   C2H5OH          +         3 O2     -->       2 CO2                         +          3 H2O

                       m = 100 g                                            m = ?

                       gfm = 46 g/mol                                gfm = 44 g/mol

Using n = m/gfm we can figure the number of moles of ethanol.  We can use this to work out the number of moles of carbon dioxideas these can be directly compared. 

                                  C2H5OH          +         3 O2     -->       2 CO2                         +          3 H2O

                      n = m/gfm                      

                      = 100/46                         

                      =2.174 moles                 

The mole ratio of ethanol to carbon dioxide is 1:2. So by multiplying our number by 2 we get the number of moles of CO2.

                                    C2H5OH          +         3 O2     -->       2 CO2                         +          3 H2O

                n = moles of C2H5OH x 2

           = 2.174 x 2

           = 4.349 moles

Now that we have the number of moles of carbon dioxide we can figure out the mass produced by using the formula m = n x gfm

                                  C2H5OH          +         3 O2     -->       2 CO2                         +          3 H2O

                                                                                    m = n x gfm                       

                                                                                        = 4.349 x 44                 

                                                                                        = 191.3 g

Therefore, the mass of carbon dioxide is produced from burning 100 grams of ethanol in oxygen is 191.3g.

Katherine M. GCSE Chemistry tutor, A Level Chemistry tutor, GCSE Biol...

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