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Ch 18: Thermal Properties of Matter
Chapter 18, Problem 18

Helium gas with a volume of 3.20 L, under a pressure of 0.180 atm and at 41.0°C, is warmed until both pressure and volume are doubled. (b) How many grams of helium are there? The molar mass of helium is 4.00 g/mol.

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First, convert the initial temperature from Celsius to Kelvin by using the formula: T(K) = T(°C) + 273.15. This will allow you to use the ideal gas law.
Apply the ideal gas law to the initial conditions to find the number of moles of helium. Use the formula: PV = nRT, where P is the pressure in atmospheres, V is the volume in liters, n is the number of moles, R is the ideal gas constant (0.0821 L·atm/mol·K), and T is the temperature in Kelvin.
Since both the pressure and volume are doubled in the final state, calculate the new pressure and volume. Then, use these values along with the initial temperature (now doubled) to find the new number of moles using the ideal gas law again.
Assuming the amount of helium does not change, set the initial moles equal to the final moles calculated and solve for the initial number of moles.
Finally, convert the moles of helium to grams using the molar mass of helium (4.00 g/mol) by multiplying the number of moles by the molar mass.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Ideal Gas Law

The Ideal Gas Law relates the pressure, volume, temperature, and number of moles of a gas through the equation PV = nRT. Here, P is pressure, V is volume, n is the number of moles, R is the ideal gas constant, and T is temperature in Kelvin. This law is fundamental for understanding how gases behave under varying conditions.
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Molar Mass

Molar mass is the mass of one mole of a substance, typically expressed in grams per mole (g/mol). For helium, the molar mass is 4.00 g/mol, which means one mole of helium weighs 4 grams. This concept is crucial for converting between the number of moles and the mass of a substance.
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Gas Laws

Gas laws describe the relationships between pressure, volume, and temperature of gases. In this scenario, both Boyle's Law (pressure and volume) and Charles's Law (temperature and volume) apply, as the gas is warmed and its volume and pressure are doubled. Understanding these laws helps predict how changes in one variable affect the others.
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Related Practice
Textbook Question
Solid water (ice) is slowly warmed from a very low temperature. (a) What minimum external pressure p1 must be applied to the solid if a melting phase transition is to be observed? Describe the sequence of phase transitions that occur if the applied pressure p is such that p < p1.
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Textbook Question
A 20.0-L tank contains 4.86 * 10^-4 kg of helium at 18.0°C. The molar mass of helium is 4.00 g/mol. (a) How many moles of helium are in the tank?
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Textbook Question
A 20.0-L tank contains 4.86 * 10^-4 kg of helium at 18.0°C. The molar mass of helium is 4.00 g/mol. (b) What is the pressure in the tank, in pascals and in atmospheres?
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Textbook Question
You have several identical balloons. You experimentally determine that a balloon will break if its volume exceeds 0.900 L. The pressure of the gas inside the balloon equals air pressure (1.00 atm). (a) If the air inside the balloon is at a constant 22.0°C and behaves as an ideal gas, what mass of air can you blow into one of the balloons before it bursts?
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Textbook Question
A large cylindrical tank contains 0.750 m^3 of nitrogen gas at 27°C and 7.50 * 10^3 Pa (absolute pressure). The tank has a tight-fitting piston that allows the volume to be changed. What will be the pressure if the volume is decreased to 0.410 m^3 and the temperature is increased to 157°C?
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Textbook Question
Oxygen (O2) has a molar mass of 32.0 g>mol. What is (e) Suppose an oxygen molecule traveling at this speed bounces back and forth between opposite sides of a cubical vessel 0.10 m on a side. What is the average force the molecule exerts on one of the walls of the container? (Assume that the molecule's velocity is perpendicular to the two sides that it strikes.)
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