1. HIGHLIGHT carbon in legend
QUESTION:
Consider the pictorial representation of a chemical change shown below. Which of the following is not a product of the reaction? A. C2H2, B. H2O, C. CO2
Consider the pictorial representation of a chemical change shown below. Which of the following is not a product of the reaction? A. C2H2, B. H2O, C. CO2
PAUSE Let’s examine the figure to see what molecules are being represented.
According to the legend, a carbon atom is represented here by a filled circle.
HIGHLIGHT carbon in legend
and a hydrogen atom is represented by a small unfilled circle.
HIGHLIGHT hydrogen in legend
Therefore, this …
CALLOUT “C2H2” pointing to one of the C2H2 molecules in before picture
is a C2H2 molecule.
We have three of this before picture.
One…
HIGHLIGHT Two…
HIGHLIGHT Three…
In the after picture, we have only one left.
HIGHLIGHT.
This means that during the reaction, the amount of C2H2 decreases.
C2H2 is being consumed. It’s a reactant.
Therefore, the correct answer is A. C2H2 is not a product of the reaction. It’s a reactant.
How about water … H2O… and carbon dioxide CO2?
Let’s see. An H2O molecule should consist of two hydrogen atoms and one oxygen atom.
According to the legend, a hydrogen atom is represented by two small unfilled circles.
… and an oxygen atom is represented by one big unfilled circle.
HIGHLIGHT oxygen in legend.
Therefore, these…
CALLOUT “H2O” pointing to water molecules
represent water molecules. We have none of these before the reaction, and two after the reaction.
Therefore, water molecules are products of this reaction.
Similarly, we can see that there are 4 CO2 molecules shown in the after picture.
HIGHLIGHT
Two…
Three…
And there is none in the before picture.
We have more CO2 after the reaction occurred. So carbon dioxide is a product.
CLICK PAUSE END RECORDING

2. Video ID: © 2008, Project VALUE (Video Assessment Library for Undergraduate Education), Department of Physical Sciences Nicholls State University Author: Glenn V. Lo Narrator: Funded by Louisiana Board of Regents Contract No. LA-DL-SELECT-13-07/08