Video Transcript
Which of the following is the best
description of standard temperature and pressure? (A) One atmosphere, 25 degrees
Celsius. (B) Zero atmospheres, zero degrees
Celsius. (C) One atmosphere, zero degrees
Celsius. (D) 25 atmospheres, one degree
Celsius. (E) Two atmospheres, 25 degrees
Celsius.
Avogadro’s law is applied to
chemistry so we can better understand the relationship between the volume of gas and
the number of moles of gas. This law states that the volume of
gas and the number of moles of a gas are directly proportional at a constant
temperature and pressure. We can represent Avogadro’s law
using the following proportionality statement. 𝑉 is proportional to 𝑛, where 𝑉
is the volume of the gas and 𝑛 is the number of moles.
For this proportion to hold true,
however, temperature and pressure must remain constant. If either temperature or pressure
change at any point during an experiment, the proportion between the volume of gas
and the number of moles of gas will also change. This important caveat to the law is
the reason why scientists felt the need to define a standard temperature and
pressure, STP, in a manner that was standardized so the value could be studied
consistently. STP defines standard temperature as
zero degrees Celsius, and standard pressure is one atmosphere, abbreviated to
atm. STP is important because it allows
scientists to obtain much more accurate and complete data and compare it to the work
of other scientists.
For example, since we know that at
STP volume and number of moles are directly proportional and that this will remain
constant, we can use a graph to predict or determine the volume at a certain number
of moles, known as the molar volume. The consistency of this rule means
that if we plot the volume versus the number of moles on a graph, the plot’s line
will be linear. And we can therefore make
predictions with which to compare experimental results accurately. However, if the conditions were not
at STP, our graph would not be linear and we could not make predictions. Through STP, we can know for
certain that we measure things like molar volume accurately and consistently.
Now let’s look at our question. Through the description, we learned
that standard temperature is defined as zero degrees Celsius and standard pressure
is one atmosphere. So, which answer choice matches our
definition? As we can see, only answer choice
(C) matches our STP definition. The correct answer is one
atmosphere, zero degrees Celsius.
