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Ch 18: Thermal Properties of Matter
Young & Freedman Calc - University Physics 14th Edition
Young & Freedman Calc14th EditionUniversity PhysicsISBN: 9780321973610Not the one you use?Change textbook
Chapter 18, Problem 25

In a gas at standard conditions, what is the length of the side of a cube that contains a number of molecules equal to the population of the earth (about 7×1097\(\times\)10^9 people)?

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First, understand that the problem involves calculating the volume of a cube that contains a specific number of molecules, equivalent to the population of the Earth, which is approximately 7 * 10^9 molecules.
Next, recall that at standard conditions (0°C and 1 atm), one mole of an ideal gas occupies 22.4 liters. Use Avogadro's number, which is approximately 6.022 * 10^23 molecules per mole, to find the volume occupied by 7 * 10^9 molecules.
Calculate the number of moles corresponding to 7 * 10^9 molecules using the formula: \( \text{Number of moles} = \frac{\text{Number of molecules}}{\text{Avogadro's number}} \).
Determine the volume occupied by these moles using the relation: \( \text{Volume} = \text{Number of moles} \times 22.4 \text{ liters/mole} \).
Finally, find the length of the side of the cube by taking the cube root of the volume in liters, since the volume of a cube is given by \( \text{Volume} = \text{side length}^3 \).

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Key Concepts

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

Avogadro's Number

Avogadro's Number is a fundamental constant in chemistry and physics, representing the number of constituent particles, usually atoms or molecules, in one mole of a substance. It is approximately 6.022 x 10^23 particles per mole. This concept is crucial for converting between the number of molecules and moles, which is necessary for calculating the volume of gas containing a specific number of molecules.
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Ideal Gas Law

The Ideal Gas Law is a fundamental equation in physics that relates the pressure, volume, temperature, and number of moles of an ideal gas. It is expressed as PV = nRT, where P is pressure, V is volume, n is the number of moles, R is the ideal gas constant, and T is temperature. This law helps determine the volume occupied by a given number of molecules under standard conditions.
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Standard Conditions

Standard conditions refer to a set of agreed-upon reference conditions for temperature and pressure used in scientific calculations. Typically, these are 0°C (273.15 K) and 1 atm pressure. Understanding standard conditions is essential for applying the Ideal Gas Law to find the volume of a gas, as it provides a baseline for calculations involving gases.
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Related Practice
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Consider an ideal gas at 2727°C and 1.001.00 atm. To get some idea how close these molecules are to each other, on the average, imagine them to be uniformly spaced, with each molecule at the center of a small cube. What is the length of an edge of each cube if adjacent cubes touch but do not overlap?

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Modern vacuum pumps make it easy to attain pressures of the order of 101310^{-13} atm in the laboratory. Consider a volume of air and treat the air as an ideal gas. How many molecules would be present at the same temperature but at 1.001.00 atm instead?

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