Consider the following intermediate chemical equations.
[tex]
\begin{array}{l}
C(s)+\frac{1}{2} O_2(g) \rightarrow CO(g) \\
CO(g)+\frac{1}{2} O_2(g) \rightarrow CO_2(g)
\end{array}
[/tex]
When you form the final chemical equation, what should you do with CO?
A. Cancel out CO because it appears as a reactant in one intermediate reaction and a product in the other intermediate reaction.
B. Add the two CO molecules together, and write them as reactants in the final chemical reaction.
C. Write CO only once as a reactant in the final chemical reaction.
D. Write CO as a reactant and a product in the final chemical reaction.
Answer (1)
To form the final chemical equation from the given intermediate equations:
Add the two equations together.
Identify that CO appears on both sides of the equation.
Cancel out CO from both sides because it is an intermediate.
The correct action is to cancel out CO because it appears as a reactant in one intermediate reaction and a product in the other intermediate reaction.
Explanation
Combining Chemical Equations We are given two intermediate chemical equations:
C ( s ) + 2 1 O 2 ( g ) → CO ( g )
CO ( g ) + 2 1 O 2 ( g ) → C O 2 ( g )
We want to combine these equations into a single, overall equation. To do this, we add the equations together, treating the arrow as an equals sign. If a substance appears on both sides of the resulting equation, we can cancel it out.
Adding the Equations Adding the two equations gives:
C ( s ) + 2 1 O 2 ( g ) + CO ( g ) + 2 1 O 2 ( g ) → CO ( g ) + C O 2 ( g )
Now, we simplify by combining like terms:
C ( s ) + O 2 ( g ) + CO ( g ) → CO ( g ) + C O 2 ( g )
Canceling Common Species Notice that CO ( g ) appears on both sides of the equation. Since it is a product in the first reaction and a reactant in the second reaction, it is an intermediate. Therefore, we can cancel it out from both sides:
C ( s ) + O 2 ( g ) → C O 2 ( g )
Final Answer The final chemical equation is:
C ( s ) + O 2 ( g ) → C O 2 ( g )
In this process, we canceled out CO because it appeared as a product in one intermediate reaction and a reactant in the other intermediate reaction.
Examples
In environmental chemistry, understanding how to combine chemical equations is crucial for modeling complex processes like the formation of acid rain. For example, sulfur dioxide ( S O 2 ) released from burning fossil fuels can react with oxygen in the atmosphere to form sulfur trioxide ( S O 3 ), which then reacts with water to form sulfuric acid ( H 2 S O 4 ). By combining these intermediate reactions, we can determine the overall impact of sulfur dioxide emissions on acid rain formation, helping us develop strategies to mitigate its effects. This process is similar to combining the given chemical equations to understand the net reaction.
