Pick the statement that describes the chemical reaction shown in the following symbolic equation: CH4 plus two O2 react to form CO2 plus two H2O. (A) Carbon dioxide reacts with water to produce methane and oxygen. (B) methane decomposes under heat to produce oxygen, carbon dioxide, and water. (C) Methane burns in carbon dioxide to produce oxygen and water. (D) Methane burns in oxygen to produce carbon dioxide and water. (E) Oxygen reacts with water to produce methane and carbon dioxide.
In this question, a symbolic equation is provided to represent a specific chemical reaction. A symbolic equation is also called a chemical equation and uses chemical symbols to represent substances involved in a reaction. For example, the first substance listed in the chemical equation, CH4, contains two chemical symbols. The chemical symbol C stands for the element carbon, and the chemical symbol H stands for hydrogen. When chemical symbols are written together with no spaces between them, they represent the chemical formula of a substance. This particular substance is a compound because it contains two or more elements in a fixed ratio. Each molecule of this compound contains one carbon atom and four hydrogen atoms. The name of this compound is methane.
Let’s begin creating a basic statement for the reaction. We can add the word methane underneath the formula CH4. Every chemical equation has three main parts: the reactants, the reaction arrow, and the products. The reactants, which are the starting materials of the reaction, appear on the left-hand side of the reaction arrow. This chemical reaction has two reactants. The first reactant is methane. Different substances in a chemical equation are separated by a plus sign. The plus sign represents the word “and.” The second reactant has a chemical formula O2. The chemical symbol O stands for the element oxygen. Each molecule of this substance contains two oxygen atoms, so its name is diatomic oxygen. However, it is typically called oxygen in statements of reactions.
Let’s add the word “oxygen” to our reaction statement. The two just to the left of the oxygen chemical formula is a coefficient used to balance the equation. The two is not part of the name, and it is also not part of the chemical formula. The reaction arrow separates the reactants from the products in a chemical equation. It is often represented with the words “reacts to produce.” The products, which are the new substances formed during a chemical reaction, appear on the right-hand side of the arrow.
There are two products in this reaction. These products contain the same three elements that were present in the reactants. The first product has a chemical formula of CO2. It is a chemical compound and has the name carbon dioxide. The second product has a chemical formula of H2O. Let’s complete our reaction statement by adding the word “and” the word “water.” The two that appears to the left of the chemical formula. H2O is a coefficient used to balance the equation and is not part of the name or the chemical formula.
Now that we have a basic statement for the reaction, let’s examine the answer choices. Let’s write an unbalanced equation for choice (A). Carbon dioxide is reacting with water, so the left side of the equation is CO2 plus H2O. Methane and oxygen are produced, so the right side of the equation is CH4 plus O2. The reactants and the products are in opposite places when compared to the given equation. So, choice (A) is an incorrect answer choice.
In choice (B), methane decomposes to produce oxygen, carbon dioxide, and water. This means methane, or CH4, is the only reactant and O2, CO2, and H2O are the products. So, answer choice (B) is also not a correct answer choice. Also, during a chemical reaction, only elements present in the reactants can be present in the products. The reactant methane only contains carbon and hydrogen, so it would not be possible to make products that contain oxygen.
Choice (C) states that methane burns in carbon dioxide. So, the left side of the equation is CH4 plus CO2. The products are O2 and H2O. In the equation provided in the question, CO2 is a product and O2 is a reactant. This means that answer choice (C) is also an incorrect answer choice.
The reactants in answer choice (D) are methane and oxygen, and the products are carbon dioxide and water. So, answer choice (D) is the correct answer choice. Although the equation we wrote does not contain the coefficients needed to balance the equation, that is okay because, in this question, we are only trying to identify which answer choice has the same reactants and products as the given equation.
In choice (E), oxygen and water are the reactants, and methane and carbon dioxide are the products. In the chemical equation provided in the question, H2O is a product, and CH4 is a reactant. This makes answer choice (E) an incorrect answer choice. Also, during a chemical reaction, only elements present in the reactants can be present in the products. The reactants O2 and H2O do not contain the element carbon, so they cannot react to form a product that contains carbon.
The statement that describes the chemical reaction shown is “methane burns in oxygen to produce carbon dioxide and water” or choice (D).