A balanced chemical equation shows the number of particles of each substance involved in a chemical reaction. Such an equation includes formulas and coefficients. A formula includes symbols for each type of atom in the substance. The coefficients are the numbers present in front of the formulae. If you are given a verbal description of a reaction, then you can identify the reactant and product formulae and write a balanced chemical equation with the formulae and some coefficients.
 

There are two questions in this Question Group. The two questions are very similar or are the same type of reaction The question below is one of the questions.
 

Version 1:
The sentence below describes a chemical reaction. Write and balance the equation for this reaction.
 
Ethanol, C2H6O, undergoes combustion.
 

To be successful with this question, you need to understand what a combustion reaction is and you need to know how to balance a chemical equation.  A combustion reaction involves the reaction of a substance with oxygen gas (O2). The most common combustible substance is a hydrocarbon - a substance containing the elements carbon and hydrogen. In this case, the substance undergoing combustion is a hydrocarbon. The products of hydrocarbon combustion are carbon dioxide (CO2) and water vapor (H2O).

Understanding this about combustion allows you to quickly get through Step 1 and Step 2 of the question. That leaves Step 3 in which you have to identify the lowest possible whole number coefficients. 

The infographic below describes a step-by-step method for balancing a chemical equation. Study the method and then prepare to apply it to this question. There are some additional specifics after the graphic that pertain specifically to this question.
 

 

Some Specifics About This Question Group

If you apply the step-by-step method to this question, then you will likely begin by balancing the element hydrogen by inserting a coefficient in front of the product H2O. And balance the element carbon by inserting a coefficeint in front of the product CO2. Finally, you will balance the oxygen by inserting a coefficient in front of the reactant O2. Then you should be done.