Standard temperature and pressure (STP) is a crucial concept in gas calculations, providing a reference point for various scientific applications. 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. 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 accurate gas law calculations.
11 Gases
Standard Temperature and Pressure
11 Gases
Standard Temperature and Pressure: Videos & Practice Problems
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.
In order to accurately study the effect that changes in pressure, temperature and moles have on volume, chemists will often run their experiments under Standard Temperature and Pressure conditions.
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Concept
Standard Temperature and Pressure
Video duration:
33sStandard Temperature and Pressure Video Summary
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Example
Standard Temperature and Pressure Example 1
Video duration:
2mStandard Temperature and Pressure Example 1 Video Summary
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 problem states that a sample of oxygen gas has a volume of 325 mL at STP. First, we need to convert the volume from milliliters to liters, which gives us 0.325 L.
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 (0.325 L)
- R = ideal gas constant (0.08206 L·atm/(mol·K))
- T = temperature (273.15 K)
Substituting the known values into the equation, we calculate the number of moles of oxygen gas:
\[n = \frac{(1 \, \text{atm})(0.325 \, \text{L})}{(0.08206 \, \text{L·atm/(mol·K)})(273.15 \, \text{K})}\]
After performing the calculation, we find that:
\[n \approx 0.01450 \, \text{moles of } O_2\]
Next, to convert moles 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 straightforward:
\[\text{mass} = n \times \text{molar mass} = 0.01450 \, \text{moles} \times 32 \, \text{g/mol} \approx 0.464 \, \text{grams of } O_2\]
Finally, rounding to three significant figures (as indicated by the original volume of 325 mL), the mass of the oxygen gas is approximately 0.464 grams. This process illustrates the relationship between volume, moles, and mass in gas calculations, emphasizing the importance of unit conversions and the ideal gas law in determining the properties of gases under specific conditions.
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Concept
Standard Temperature and Pressure
Video duration:
1mStandard Temperature and Pressure Video Summary
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 equation simplifies as the units for moles, temperature, and pressure cancel out, leading to a volume of:
22.4 \(\text{ liters}\)
This value, 22.4 liters, is significant as it establishes a direct conversion factor: for any ideal gas at STP, one mole will occupy 22.4 liters. This relationship is essential for calculations involving gas volumes and moles, allowing for straightforward conversions in stoichiometric calculations and gas law applications.
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Example
Standard Temperature and Pressure Example 2
Video duration:
1mStandard Temperature and Pressure Example 2 Video Summary
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 as follows:
Number of moles (n) = Volume (V) / Molar volume = 15.7 L / 22.4 L/mol
When we perform this calculation, we find:
n = 0.70 moles of Cl2
Alternatively, we can use the ideal gas law, represented by the equation:
PV = nRT
In this equation, P is the pressure (1 atmosphere at STP), V is the volume (15.7 liters), n is the number of moles, R is the ideal gas constant (0.0821 L·atm/(K·mol)), and T is the temperature (273.15 K 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)
After performing this calculation, we also arrive at:
n = 0.70 moles of Cl2
Both methods yield the same result, demonstrating that we can approach gas calculations using either the standard molar volume or the ideal gas law, depending on the information available.
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Problem
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
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Problem
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
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Problem
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
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Standard temperature and pressure (STP) is a set of conditions commonly used in chemistry to describe gases. STP is defined as a temperature of 0 degrees Celsius, which is equivalent to 273.15 Kelvin, and a pressure of 1 atmosphere (atm). These conditions provide a reference point for comparing gas behaviors and performing calculations. Using STP allows chemists to standardize measurements and easily calculate properties like volume, pressure, and temperature of gases under consistent conditions.
The standard molar volume of an ideal gas at STP is the volume occupied by one mole of gas under standard temperature and pressure conditions. It is calculated using the ideal gas law equation: , where is volume, is moles, is the ideal gas constant, is temperature in Kelvin, and is pressure. At STP, with , K, and , the volume is found to be 22.4 liters. This is the standard molar volume of an ideal gas at STP.
The Kelvin scale is used in gas law calculations because it is an absolute temperature scale starting at absolute zero, where molecular motion theoretically stops. Unlike Celsius, Kelvin does not have negative values, which is important for gas laws that involve temperature ratios and direct proportionality. Using Kelvin ensures that temperature values are always positive, making calculations consistent and physically meaningful. At STP, the temperature is 273.15 K, which corresponds to 0 °C, but Kelvin is preferred for all gas law equations.
The ideal gas law relates the number of moles (), volume (), temperature (), and pressure () of a gas through the equation . At STP, the temperature is fixed at 273.15 K and pressure at 1 atm, so the volume of a gas is directly proportional to the number of moles. This relationship allows us to calculate the volume occupied by any amount of gas at STP or to find the number of moles if volume is known. It is fundamental for understanding gas behavior under standard conditions.
The standard molar volume of 22.4 liters is significant because it represents the volume occupied by one mole of an ideal gas at standard temperature and pressure (0 °C and 1 atm). This value provides a convenient conversion factor between moles and volume for gases under these conditions. It simplifies calculations in stoichiometry, gas reactions, and laboratory measurements by allowing chemists to easily convert between the amount of gas in moles and its volume in liters. This standardization is essential for comparing experimental results and theoretical predictions.
