Video Transcript
In the following reaction, the rate
of sulfur formation was determined to be 0.002 grams per second. Na2S2O3 aqueous plus two HCl
aqueous reacts to form two NaCl aqueous plus H2O liquid plus SO2 gas plus S
solid. How much sulfur was formed after
five minutes?
In this reaction, sodium
thiosulfate reacts with hydrochloric acid to form sodium chloride, water, sulfur
dioxide gas, and sulfur. We’ve been asked to determine how
much sulfur is formed, and we were given the rate of sulfur formation. The rate of sulfur formation is the
rate of this reaction. Looking at the units, we can see
that the rate is by mass. The rate of a chemical reaction can
be defined in terms of the formation of a product or the consumption of a
reactant. The Δ symbol here indicates a
change in, so the rate of reaction for the mass is the change in mass divided by the
change in time.
We’re interested in sulfur for this
question, which is a product. So we’ll use the formula for the
rate of reaction that corresponds to the formation of a product. We need to come up with a formula
that we can use to calculate the mass of sulfur. We can do that if we multiply both
sides of the rate equation by the change in time. If we do, we’ll end up with the
equation here.
Now we can solve for the amount of
sulfur that was formed. The problem gave us the rate; it’s
0.002 grams per second. The time given in the problem is
five minutes. But the rate is given in units of
seconds, and the units here need to match. We can convert the time into
seconds if we multiply by 60, because there are 60 seconds in one minute. That will give us 300 seconds.
Now we can finish the problem and
solve for the mass of sulfur. The units of seconds cancel, and we
get 0.6 grams. So 0.6 grams of sulfur was formed
after five minutes.
