Video Transcript
Consider the following
reaction. C3H4 plus three O2 react to produce
two x plus two y plus z. Which chemicals replace x, y, and z
in the correct order to balance this incomplete combustion of propyne? (A) CO2 gas, H2O liquid, carbon
solid. (B) CO2 gas, carbon solid, H2O
liquid. (C) CO gas, carbon solid, H2O
liquid. (D) CO gas, H2O liquid, carbon
solid. (E) CO2 gas, CO gas, H2O
liquid.
In this question, we are being
asked to determine the identities of the substances x, y, and z, which are products
of the provided reaction. Propyne, or C3H4, is a hydrocarbon
and can burn in the presence of oxygen gas in a type of reaction called
combustion. Some of the factors which influence
the type of products formed in a combustion reaction are the type and size of the
hydrocarbon molecules, the availability of oxygen, and temperature. In the complete combustion of a
hydrocarbon, the only products are carbon dioxide and water.
However, we are told that the
reaction taking place is incomplete combustion. The general equation below
represents the incomplete combustion of a hydrocarbon. Water is still produced, but carbon
monoxide gas and carbon soot are produced instead of carbon dioxide. However, there are plenty of
examples of incomplete combustion that involve other combinations of carbon-based
products. For example, in the incomplete
combustion of propane, only carbon soot and water may be formed. So, we can’t just use the general
equation to predict what the products will be. However, we do know one of the
products must be water because it is found in all of the answer choices. Instead, we will need to use the
coefficients provided for the products to help us solve the problem.
Let’s begin by examining the
reactant side of the chemical equation. Since this part of the equation is
already balanced, we know we have three carbon atoms, four hydrogen atoms, and six
oxygen atoms. This means that water must either
be substance x or substance y because only these two possibilities would give us a
total of four hydrogen atoms on the product side. Knowing this allows us to eliminate
answer choices (B), (C), and (E) because these answer choices list water as product
z.
Next, let’s consider the number of
oxygen atoms. We know that the sum of oxygen
atoms in all of the products must equal six. Let’s consider answer choice (D)
first. If x is carbon monoxide and z is
carbon soot, then there are only four oxygen atoms on the right side of the
equation, which is not enough. Therefore, answer choice (D) cannot
be the correct answer.
Now, let’s confirm that answer
choice (A) is the correct answer. If x is carbon dioxide and z is
carbon soot, then the total number of oxygen atoms on the product side is six. And the total number of carbon
atoms will be three. In conclusion, the chemicals that
replace x, y, and z in the correct order to balance this incomplete combustion of
propyne are CO2 gas, H2O liquid, and carbon solid, or answer choice (A).
