Standard Temperature and Pressure - Online Tutor, Practice Problems & Exam Prep

Standard temperature and pressure (STP) is defined as 0 degrees Celsius (273.15 Kelvin) and 1 atmosphere of pressure. At STP, the standard molar volume of an ideal gas is 22.4 liters, which establishes a crucial relationship between moles and volume. The equation for volume is $V=nRT/P$, where n is the number of moles, R is the ideal gas constant, T is temperature, and P is pressure. This relationship is essential for gas calculations in chemistry.

Standard Temperature and Pressure

Standard temperature and pressure, abbreviated as STP, is a commonly used term in calculations involving gases. Now we're going to say at STP, the temperature is measured as either 0 degrees Celsius or 273.15 Kelvin. Now we know that when we're dealing with gas calculations, we tend to go with Kelvin. Now the pressure at STP is 1 atmosphere. So just remember, when you hear STP, it means 273.15 Kelvin and for pressure, 1 atmosphere.

Standard Temperature and Pressure Example 1

Here in this example question, it says, a sample of oxygen gas has a measured volume of 325 mL at STP. How many grams are present? Alright. So here they're giving us the volume in the form of milliliters, and STP is giving us temperature plus pressure. We know from the ideal gas law with these values given to us or these variables given to us, the only thing that's missing is our moles because we have volume already, we have pressure and temperature, and we always know what R is. So we're going to divide up RT and when we do that we're going to get our moles. Moles here will equal pressure times volume over R times T. At STP, our pressure is 1 atmosphere. Our volume, we just change milliliters to liters, so 0.325 liters. We have our R constant which is 0.08206 liters times atmospheres over moles times K. Then remember we're dealing with temperature at STP, we use the units of Kelvin, so that's 273.15 Kelvin. So here, Kelvins cancel out, liters cancel out, atmospheres cancel out, and we'll be left with the moles of our oxygen gas. When we plug that in, we get 0.01450 moles of O₂. But here the question is not asking us to determine the moles of oxygen gas, but instead the grams of oxygen gas. So we just need to do a simple conversion. We say that for every 1 mole of O₂ it weighs 32 grams because there are 2 oxygens. Those cancel out and what we get at the end is 0.464 grams of O₂. Here our answer has 3 significant figures because the value of 325 has 3 significant figures as well. So just the value that's missing is moles. Then go for moles that the value that's missing is moles. Then go from moles to grams to get your final answer.

Standard Temperature and Pressure

With the idea of STP, we are faced with a new idea, the standard molar volume. Now we're going to say that it represents the volume of 1 mole of an ideal gas at STP. Alright. So here we're gonna say V=n⋅R⋅T/P. We're dealing with 1 mole of the gas, R is just our constant, and we're gonna say we're dealing with STP, so our temperature will be 273.15 Kelvin, and our pressure will just simply be 1 atmosphere. We see here that the moles cancel out, kelvins cancel out, atmospheres cancel out. So here we'll have our volume in liters. When we plug this in we get 22.4 liters. This would represent our standard molar volume for 1 mole of gas, an ideal gas. Now this helps to establish a relationship between moles and volumes, and because we have a relationship between moles and volumes, we can create a new conversion factor, and that conversion factor would be that for any one mole of an ideal gas at STP, its molar volume would be 22.4 liters. So just remember, if we're dealing with STP and we're dealing with 1 mole of any gas, then its standard molar volume will be 22.4 liters.

Standard Temperature and Pressure Example 2

Here the example question asks, "How many moles of chlorine gas occupy a volume of 15.7 liters at STP?" Alright. So here they're talking about determining the moles of an ideal gas. They're giving us the volume of that gas at STP. Here we can use the conversion factor that we know exists with standard molar volume. We're going to say we have 15.7 liters and we're going to say here that the conversion factor is for every 1 mole of any gas at STP, the volume is 22.4 liters. Here, liters cancel out and I have my moles, which comes out to 0.70 moles of Cl₂. So this is one way that we get our answer.

What else we could do is we could have also said that we have 15.7 liters which is our volume, and then we have STP which is pressure and temperature. We could have said that our moles equals PVRT and we would have gotten the same exact answer because here this would have been 1 atmosphere. This here is 15.7 liters. Then here we have our R constant with its units, don't forget the units, times temperature at STP is 273.15 Kelvin. And if we worked it out we get the same exact moles for Cl₂. So just realize that there are 2 ways that we can approach a question like this, using it with the conversion factor of 1 mole for every 22.4 liters, or by using it through the traditional means with the ideal gas law.

A sample of dichloromethane gas (CH₂Cl₂) occupies 32.6 L at 310 K and 5.30 atm. Determine its volume at STP?

• A. 145 L
• B. 150 L
• C. 320 L
• D. 350 L
• E. 390 L

Which gas sample has the greatest volume at STP?

• A. 10.0 g He
• B. 10.0 g Ne
• C. 10.0 g N
• D. All have the same volume

Nitrogen and hydrogen combine to form ammonia via the following reaction:

                      1 N₂ (s)  +  3 H₂ (g) → 2 NH₃ (g)

What mass of nitrogen is required to completely react with 800.0 mL H₂ at STP?

• A. 0.333 g
• B. 0.512 g
• C. 0.802 g
• D. 1.01 g
• E. 1.36 g

Here’s what students ask on this topic:

What is Standard Temperature and Pressure (STP) in chemistry?

Standard Temperature and Pressure (STP) in chemistry is a set of conditions used for gas calculations. STP is defined as a temperature of 0 degrees Celsius (273.15 Kelvin) and a pressure of 1 atmosphere. These conditions are used to standardize measurements and calculations involving gases, making it easier to compare different sets of data.

How do you calculate the volume of a gas at STP?

To calculate the volume of a gas at STP, you can use the ideal gas law equation: $V=\frac{nRT}{P}$. Here, $V$ is the volume, $n$ is the number of moles, $R$ is the ideal gas constant (0.0821 L·atm/(K·mol)), $T$ is the temperature in Kelvin (273.15 K at STP), and $P$ is the pressure (1 atm at STP). For 1 mole of an ideal gas at STP, the volume is 22.4 liters.

What is the standard molar volume of an ideal gas at STP?

The standard molar volume of an ideal gas at STP is 22.4 liters. This means that one mole of any ideal gas occupies 22.4 liters of volume at a temperature of 0 degrees Celsius (273.15 Kelvin) and a pressure of 1 atmosphere. This value is derived from the ideal gas law and is a useful conversion factor in gas calculations.

Why is STP important in gas calculations?

STP is important in gas calculations because it provides a standardized set of conditions (0 degrees Celsius and 1 atmosphere) that allow for consistent and comparable measurements. Using STP simplifies calculations and conversions involving gases, such as determining the volume, pressure, or temperature of a gas sample. It also helps in understanding the behavior of gases under these standard conditions.

How does the ideal gas law relate to STP?

The ideal gas law, given by the equation $\mathrm{PV}=\mathrm{nRT}$, relates pressure (P), volume (V), number of moles (n), the ideal gas constant (R), and temperature (T). At STP, the temperature is 273.15 K and the pressure is 1 atm. By substituting these values into the ideal gas law, we can determine the volume of one mole of an ideal gas at STP, which is 22.4 liters. This relationship is crucial for understanding gas behavior under standard conditions.