Standard Temperature and Pressure: Videos & Practice Problems

Standard Temperature and Pressure (STP) is crucial for gas calculations, defined as 0°C (273.15 Kelvin) and 1 atmosphere of pressure. At STP, one mole of an ideal gas occupies a standard molar volume of 22.4 liters. This establishes a direct relationship between the amount of gas in moles and its volume in liters, serving as a conversion factor for gas-related computations. Remember, the volume of any ideal gas at STP can be determined using the equation:

$V=nRT/P$

where '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.

Standard Temperature and Pressure

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 Kelvin and a pressure of 1 atmosphere, which are essential for accurately applying gas laws and performing calculations in chemistry.

STP Calculation Example

To determine the mass of oxygen gas from a given volume at standard temperature and pressure (STP), we can utilize the ideal gas law. The ideal gas law states that the number of moles (n) can be calculated using the formula:

n = \frac{PV}{RT}

In this equation, P represents pressure, V is volume, R is the ideal gas constant, and T is temperature. At STP, the pressure (P) is 1 atmosphere, and the temperature (T) is 273.15 Kelvin. The volume provided is 325 milliliters, which we need to convert to liters:

V = 325 \, \text{ml} = 0.325 \, \text{liters}

The ideal gas constant (R) is 0.08206 L·atm/(mol·K). Now, substituting the known values into the equation:

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

After performing the calculations, we find:

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

Next, to convert moles of oxygen gas to grams, we use the molar mass of oxygen. The molar mass of O₂ is 32 grams per mole (since each oxygen atom has a mass of approximately 16 grams, and there are two atoms in a molecule of O₂). Thus, the conversion is as follows:

\text{mass} = n \times \text{molar mass} = 0.01450 \, \text{moles} \times 32 \, \text{g/mol} \approx 0.464 \, \text{grams of } O_2

Finally, considering significant figures, the answer is reported as 0.464 grams of O₂, matching the three significant figures of the initial volume measurement.

Standard Molar Volume

At standard temperature and pressure (STP), the concept of standard molar volume is introduced, which defines the volume occupied by one mole of an ideal gas. The relationship can be expressed using 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. At STP, the temperature is set at 273.15 K and the pressure at 1 atmosphere. When we consider 1 mole of gas, the equation simplifies as the moles cancel out, leading to a calculation of volume in liters.

Upon substituting the values into the equation, we find that the volume is 22.4 liters. This value represents the standard molar volume for one mole of an ideal gas at STP. Consequently, this establishes a crucial conversion factor: for any ideal gas at STP, one mole will occupy a volume of 22.4 liters. Therefore, it is essential to remember that at STP, the standard molar volume for one mole of any gas is consistently 22.4 liters.

Moles of Gas Example

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 properties of ideal gases.

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:

Number of moles = Volume (liters) / Molar volume (liters/mole) = 15.7 L / 22.4 L/mol

When we perform this calculation, we find that:

Number of moles = 0.70 moles of Cl₂

Alternatively, we can use 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 Kelvin at STP)

Rearranging the equation to solve for n gives us:

n = PV / RT

Substituting the known values:

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

Upon calculating this, we also arrive at:

n = 0.70 moles of Cl₂

Both methods yield the same result, demonstrating that we can effectively determine the number of moles of a gas at STP either through the standard molar volume or by applying 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

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

Answer: (A)

Here’s what students ask on this topic:

What is standard temperature and pressure (STP)?

Standard Temperature and Pressure (STP) is a reference point used in chemistry to provide a set of conditions for experiments and calculations. At STP, the standard temperature is defined as 0 degrees Celsius (273.15 Kelvin), and the standard pressure is 1 atmosphere (atm), which is equivalent to 101.325 kilopascals (kPa). These conditions are important because they provide a baseline that can be used to compare different chemical reactions and properties of substances. For instance, at STP, one mole of an ideal gas occupies 22.414 liters of volume. This reference is crucial for calculations involving gas laws and behaviors under controlled conditions. It's essential to note that STP is different from the standard ambient temperature and pressure (SATP), which uses a temperature of 25 degrees Celsius and a pressure of 100 kPa.

What volume will one mole of a gas occupy under standard temperature and pressure?

Under standard temperature and pressure (STP), which is defined as a temperature of 0°C (273.15 K) and a pressure of 1 atmosphere (atm), one mole of an ideal gas occupies a volume of 22.414 liters. This is known as the molar volume of a gas, and it's a consequence of the Ideal Gas Law when applied to STP conditions. The Ideal Gas Law is:

$PV=nRT$

where P is the pressure, V is the volume, n is the number of moles, R is the ideal gas constant, and T is the temperature in Kelvin. When you plug in the values for STP (P = 1 atm, T = 273.15 K, and n = 1 mole), and use the appropriate value for R (0.0821 L·atm/mol·K), you can solve for V, which gives you the volume of the gas.

What are the standard temperature and pressure values for sea level?

Standard temperature and pressure (STP) values for sea level are commonly used as reference points in physics and chemistry. The standard temperature is defined as 0 degrees Celsius (273.15 Kelvin), which is the freezing point of water. The standard pressure is defined as 1 atmosphere (atm), which is equivalent to 101.325 kilopascals (kPa) or 760 millimeters of mercury (mmHg). These values are important because they provide a baseline for scientists and engineers to compare different sets of experimental data. When working with gases, for example, STP conditions allow for the use of the Ideal Gas Law to predict the behavior of a gas under these standard conditions.