Standard Temperature and Pressure: Videos & Practice Problems

Standard temperature and pressure (STP) defines conditions of 273.15 K and 1 atmosphere pressure, essential for gas law calculations. The standard molar volume is the volume occupied by one mole of an ideal gas at STP, calculated using the ideal gas law: $V=\frac{\mathrm{nRT}}{P}$. At STP, this volume equals 22.4 liters, establishing a key conversion factor between moles and volume for gases, facilitating understanding of gas behavior under standard conditions.

Standard Temperature and Pressure Concept 1

Standard temperature and pressure (STP) is a crucial concept in gas calculations, providing a reference point for various scientific measurements. At STP, the temperature is defined as 0 degrees Celsius, which is equivalent to 273.15 Kelvin. It is important to use Kelvin for gas calculations, as it is the absolute temperature scale. Additionally, the pressure at STP is set at 1 atmosphere (atm). Therefore, when referring to STP, remember that it signifies a temperature of 273.15 K and a pressure of 1 atm, which are essential for accurately applying gas laws and performing calculations in chemistry.

Standard Temperature and Pressure Example 1

To determine the mass of oxygen gas present in a sample with a volume of 325 mL at standard temperature and pressure (STP), we can utilize the ideal gas law. At STP, the pressure is 1 atmosphere, and the temperature is 273.15 Kelvin. The ideal gas law can be expressed as:

\[ n = \frac{PV}{RT} \]

Where:

• n = number of moles
• P = pressure (1 atm)
• V = volume in liters (0.325 L)
• R = ideal gas constant (0.08206 L·atm/(mol·K))
• T = temperature in Kelvin (273.15 K)

First, convert the volume from milliliters to liters:

\[ V = 325 \, \text{mL} = 0.325 \, \text{L} \]

Next, substitute the values into the equation to find the number of moles:

\[ n = \frac{(1 \, \text{atm})(0.325 \, \text{L})}{(0.08206 \, \text{L·atm/(mol·K)})(273.15 \, \text{K})} \]

Calculating this gives:

\[ n \approx 0.01450 \, \text{moles of } O_2 \]

To convert moles to grams, use the molar mass of oxygen gas (O₂), which is 32 grams per mole:

\[ \text{mass} = n \times \text{molar mass} \]

\[ \text{mass} = 0.01450 \, \text{moles} \times 32 \, \text{g/mol} \]

This results in:

\[ \text{mass} \approx 0.464 \, \text{grams of } O_2 \]

When considering significant figures, the final answer should reflect three significant figures, resulting in:

\[ \text{mass} \approx 0.464 \, \text{grams of } O_2 \]

In summary, by applying the ideal gas law and converting moles to grams, we find that a sample of oxygen gas with a volume of 325 mL at STP contains approximately 0.464 grams of O₂.

Standard Temperature and Pressure Concept 2

In the context of standard temperature and pressure (STP), the concept of standard molar volume is crucial for understanding the behavior of gases. Standard molar volume refers to the volume occupied by one mole of an ideal gas at STP, which is defined as a temperature of 273.15 Kelvin and a pressure of 1 atmosphere.

The relationship between volume, moles, and the ideal gas law can be expressed with the formula:

V = n \cdot \frac{RT}{P}

In this equation, V represents volume, n is the number of moles, R is the ideal gas constant, T is the temperature in Kelvin, and P is the pressure in atmospheres. When we consider 1 mole of an ideal gas at STP, the moles cancel out, and we can simplify the equation to find the volume:

V = \frac{RT}{P}

Substituting the values for R (0.0821 L·atm/(K·mol)), T (273.15 K), and P (1 atm), we find that the volume is:

V = 0.0821 \cdot 273.15 / 1 = 22.4 \text{ liters}

This result indicates that the standard molar volume of an ideal gas at STP is 22.4 liters. This value serves as a vital conversion factor, allowing for the conversion between moles and volume for any ideal gas under these conditions. Therefore, whenever dealing with 1 mole of an ideal gas at STP, one can confidently use the standard molar volume of 22.4 liters.

Standard Temperature and Pressure Example 2

To determine the number of moles of chlorine gas (Cl₂) occupying a volume of 15.7 liters at standard temperature and pressure (STP), we can utilize two different methods based on the principles of gas laws.

The first method involves using the standard molar volume of an ideal gas, which is 22.4 liters per mole at STP. By applying this conversion factor, we can calculate the moles of Cl₂ as follows:

Given:

Volume (V) = 15.7 liters

Conversion factor = 1 mole / 22.4 liters

Calculating moles:

moles = 15.7 liters × (1 mole / 22.4 liters) = 0.701 moles of Cl₂

The second method employs the ideal gas law, represented by the equation:

PV = nRT

Where:

• P = pressure (1 atmosphere at STP)
• V = volume (15.7 liters)
• n = number of moles
• R = ideal gas constant (0.0821 L·atm/(K·mol))
• T = temperature (273.15 K at STP)

Rearranging the equation to solve for n gives:

n = PV / RT

Substituting the known values:

n = (1 atm) × (15.7 L) / (0.0821 L·atm/(K·mol) × 273.15 K)

Calculating this yields:

n ≈ 0.701 moles of Cl₂

Both methods yield the same result, demonstrating that we can determine the number of moles of a gas at STP either through the standard molar volume or by applying the ideal gas law. Understanding these approaches is essential for solving gas-related problems in chemistry.

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

Answer: (B)

Which gas sample has the greatest volume at STP?

• A. 10.0 g He
• B. 10.0 g Ne
• C. 10.0 g N₂
• D. All have the same volume

Answer: (A)

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. 0.3330 g
• B. 0.5121 g
• C. 0.8025 g
• D. 1.018 g
• E. 1.369 g

Answer: (A)

Here’s what students ask on this topic:

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

Standard Temperature and Pressure (STP) is a set of conditions commonly used in gas calculations to provide a reference point. STP is defined as a temperature of 273.15 Kelvin (which is equivalent to 0 degrees Celsius) and a pressure of 1 atmosphere (atm). These conditions allow chemists to compare gas volumes and behaviors under consistent parameters. Using STP simplifies calculations involving gases, especially when applying the ideal gas law or determining molar volumes.

Why is temperature measured in Kelvin at STP instead of Celsius?

Temperature is measured in Kelvin at STP because the Kelvin scale is an absolute temperature scale starting at absolute zero, where molecular motion theoretically stops. This makes Kelvin the preferred unit for gas law calculations, as many gas equations, including the ideal gas law, require absolute temperature to maintain proportionality. Celsius can be negative, which would cause errors in calculations. At STP, the temperature is 273.15 K, corresponding to 0 °C, ensuring accurate and consistent results in gas-related computations.

What is the standard molar volume of an ideal gas at STP and how is it calculated?

The standard molar volume of an ideal gas at STP is 22.4 liters. This volume represents the space occupied by one mole of any ideal gas at standard temperature (273.15 K) and pressure (1 atm). It is calculated using the ideal gas law formula: $V=n\cdot \frac{R\cdot T}{P}$, where $n$ is the number of moles (1 mole), $R$ is the gas constant, $T$ is temperature in Kelvin, and $P$ is pressure in atmospheres. Plugging in the values for STP yields 22.4 liters.

How does the concept of standard molar volume help in converting between moles and volume of gases?

The concept of standard molar volume provides a direct conversion factor between the amount of gas in moles and its volume at STP. Since one mole of an ideal gas occupies 22.4 liters at STP, you can easily convert moles to volume by multiplying the number of moles by 22.4 liters. Conversely, to find moles from a given volume at STP, divide the volume by 22.4 liters. This relationship simplifies calculations in stoichiometry and gas law problems, allowing quick and accurate conversions without needing to repeatedly apply the ideal gas law.

What is the significance of using 1 atmosphere as the standard pressure in STP?

Using 1 atmosphere as the standard pressure in STP provides a consistent and widely accepted reference point for gas calculations. One atmosphere corresponds to the average atmospheric pressure at sea level, making it a practical and relatable standard. This standardization allows chemists to compare gas behaviors and volumes under uniform pressure conditions. It also simplifies calculations involving the ideal gas law, as pressure values are consistent and predictable, ensuring reliable and reproducible results in experiments and theoretical work.