Question Video: Identifying the Conditions for Standard Temperature and Pressure | Nagwa Question Video: Identifying the Conditions for Standard Temperature and Pressure | Nagwa

# Question Video: Identifying the Conditions for Standard Temperature and Pressure Chemistry • First Year of Secondary School

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Which of the following is the best description of standard temperature and pressure? [A] 1 atm, 25°C [B] 0 atm, 0°C [C] 1 atm, 0°C (D) 25 atm, 1°C [E] 2 atm, 25°C

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### 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.

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