This is an oxidation-reduction (redox) reaction:

4 C-II - 2 e- → 4 C-3/2 (oxidation)

2 HI + 2 e- → 2 H0 (reduction)

This is a gas evolution reaction, C4H6 and H2 is the formed gas.

## Word equation

Ethanol → 1,3-butadiene + hydrogen + water

## Input interpretation

CH3CH2OH → CH2=CHCH=CH2 + H2 + H2O

## Balanced equation

Balance the chemical equation algebraically:

CH3CH2OH → CH2=CHCH=CH2 + H2 + H2O

Add stoichiometric coefficients, c1, to the reactants and products:

c1CH3CH2OH → c2CH2=CHCH=CH2 + c3 H2+ c4H2O

Set the number of atoms in the reactants equal to the number of atoms in the products for C, H and O:

C: 2c1= 4c2

H: 6 c1= 6 c2+ 2 c3 + 2 c4

O: c1= c4

Since the coefficients are relative quantities and underdetermined, choose a coefficient to set arbitrarily. To keep the coefficients small, the arbitrary value is ordinarily one. For instance, set c2 = 1 and solve the system of equations for the remaining coefficients:

c1=2

c2 = 1

c3 = 1

c4=2

Substitute the coefficients into the chemical reaction to obtain the balanced equation: