This is an **oxidation-reduction** (redox) reaction:

*4* **C**-II - *2* **e**- → *4* **C**-3/2 *(oxidation)*

*2* **H**I + *2* **e**- → *2* **H**0 *(reduction)*

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

## Word equation

** ****Ethanol → 1,3-butadiene + hydrogen + water**

## Input interpretation

** C****H****3****C****H****2****OH → C****H****2****=CHCH=C****H****2**** + ****H****2**** + ****H****2****O**

** **** Ethanol 1,3-butadiene hydrogen ****water**

** **

## Balanced equation

Balance the chemical equation algebraically:

** C****H****3****C****H****2****OH → C****H****2****=CHCH=C****H****2**** + ****H****2**** + ****H****2****O**

Add stoichiometric coefficients, **c****1**, to the reactants and products:

** ****c****1****C****H****3****C****H****2****OH → ****c****2****C****H****2****=CHCH=C****H****2**** +**** c****3** **H****2****+ ****c****4****H****2****O**

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

** C: 2****c****1****= 4****c****2**

** H: 6 ****c****1****= 6 ****c****2****+ 2 ****c****3** **+ 2 ****c****4**

** O: ****c****1****= ****c****4**

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 **c****2** = 1 and solve the system of equations for the remaining coefficients:

** ****c****1****=2**

** ****c****2**** = 1 **

** ****c****3**** = 1**

** ****c****4****=2**

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

**Answer:**

** 2 C****H****3****C****H****2****OH → C****H****2****=CHCH=C****H****2**** + ****H****2**** + ****2H****2****O**