Question

hi ya'll! so my questions is that why at times do the moecules of a certain element change in different reaction.
like example- C+H2O-->CO+H
but then-Fe2O3+ 3C ---> 2Fe + 3CO.


now why is a 3 given for carbon in the latter????​

Answer 1

ANSWER:

according to LAW OF CONSERVATION OF MASS

mass can never be created and nor be destroyed in a chemical reaction.

So carbon has a mas of 12

oxygen has a mass of 16

and Fe(iron) has a mass of 56

and hydrogen has a mass of 1

so by 1st reaction:

C + H2O ----> CO + H2

(hydrogen can never be in it's elemental form so please recheck the question, it must have been H2 in place of H)

so if we calculate the mass of both side

LHS

C + H2O

12 + 1(2)+ 16

= 30

RHS

CO + H2

12+16+ 1(2)

=30

Since LHS = RHS hence in 1st reaction law of conservation of mass is obeyed

For 2nd reaction:

Fe2O3 + C -----> Fe + CO

here you can notice that the reaction aren't represented with coefficient ( i.e. the 2 and 3 before Fe and CO)

now if we calculate their masses of LHS and RHS

LHS = 56(2)+16(3) + 12

= 172

RHS= 56 + 12+16= 84

here LHS is not equal to RHS

So the law of conservation of mass is not obeyed

but we know that law of conservation of mass is universal

so we need to correct the reaction

BUT there is a problem as we cannot change the compounds ( i.e. we cannot write Fe2O3 as Fe3O4) because then it will become a different thing with other properties.

So what we can do is that add numbers to balance the reaction

Firstly let's talk about a simple reaction

H2 + O2 -----> H2O

Here you can see there are 2 oxygens in reactants sides but only one oxygen in product

we can simply tell without calculating that the above reaction is not obeying law of conservation of mass because the oxygens are unequal.

so to equate the oxygens we can write 2 in front of H2O to make it 2 oxygens in product .

H2+O2 ----> 2H2O

hence now oxygens are balanced

but in balancing oxygen, hydrogen becomes unbalanced( 2 in reactants and 4 in product)

so now we add 2 in front of hydrogen in reactants

2H2 + O2----> 2H2O

here is the balanced reaction

Similarily you can balance

Fe2O3 + C -----> Fe + CO

Just try it

What actually means from the 3 and 2 in front of CO and Fe respectively is that to react with one molecule of Fe2O3 you need to have 3 Carbon atoms and in product we will get 2 molecules of Fe and 3 molecules of Carbon Monoxide

HOPE IT HELPS YOU. :)

PLEASE MARK BRAINLIEST