A lonely party balloon with a volume of L and containing mol of air is left behind to drift in the temporarily uninhabited and depressurized International Space Station. Sunlight coming through a porthole heats and explodes the balloon, causing the air in it to undergo a free expansion into the empty station, whose total volume is m3. Calculate the entropy change of the air during the expansion.
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Problem 60b
Textbook Question
Suppose that you repeatedly shake six coins in your hand and drop them on the floor. Construct a table showing the number of microstates that correspond to each macrostate. What is the probability of obtaining six heads?

1
Understand the problem: A macrostate refers to the observable outcome (e.g., the number of heads), while a microstate refers to the specific arrangement of the coins (e.g., HHTTHT). The goal is to calculate the number of microstates for each macrostate and determine the probability of obtaining six heads.
Step 1: Use the binomial coefficient formula to calculate the number of microstates for each macrostate. The formula is: , where n is the total number of coins (6 in this case), and k is the number of heads.
Step 2: Construct a table for all possible macrostates (0 heads, 1 head, ..., 6 heads). For each macrostate, calculate the number of microstates using the binomial coefficient formula. For example, for 0 heads, the number of microstates is , and for 6 heads, it is .
Step 3: Calculate the total number of microstates by summing up the microstates for all macrostates. This total is equal to , since each coin has two possible outcomes (heads or tails).
Step 4: To find the probability of obtaining six heads, divide the number of microstates corresponding to six heads by the total number of microstates. The probability is given by: .

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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Microstates and Macrostates
In statistical mechanics, a microstate refers to a specific detailed configuration of a system, while a macrostate is defined by macroscopic properties like temperature or pressure. For example, when tossing coins, each unique arrangement of heads and tails represents a microstate, whereas the overall count of heads (e.g., six heads) represents a macrostate. Understanding the relationship between these concepts is crucial for calculating probabilities.
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Combinatorial Analysis
Combinatorial analysis involves counting the number of ways to arrange or select items from a set. In the context of the coin toss, it helps determine how many different microstates correspond to a given macrostate, such as six heads. The formula for combinations, often denoted as 'n choose k', is essential for calculating these arrangements, where 'n' is the total number of items and 'k' is the number of selected items.
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Probability
Probability quantifies the likelihood of an event occurring, expressed as a ratio of favorable outcomes to the total number of possible outcomes. In this scenario, to find the probability of obtaining six heads when tossing six coins, one must divide the number of favorable microstates (which is one, as there is only one way to get all heads) by the total number of microstates (which is 2^6, or 64). This concept is fundamental for understanding outcomes in random experiments.
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