CHEM 361 Assignment 15 (OUT OF 8PTS) Please complete this assignment before the

Question

CHEM 361 Assignment 15 (OUT OF 8PTS) Please complete this assignment before the next class meeting. Written answers to questions must be handed in at the beginning of class Read section 1.13 in the textbook. II. Answer the following questions. You are asked to consider the questions below in preparation to class discussion. Any questions you have about this homework assignment can be directed to me or your classmates. The answers to most of these questions will be clear after you read the section in the textbook specified in part l. For some of the questions, you will have to draw on your previous knowledge of chemistry You are encouraged to discuss this assignment with me and your classmates. However, the answers you hand in must be your own work. 1. Explain how attractive forces between molecules decrease the pressure of a as 2. The constants a and b in the van der Waals equation are empirical coefficients. Explain what that means. 3. Show that the units for a and b are appropriate for the van der Waals equation. 4. Under which conditions are gases most likely to act as perfect gases? Explain.

Explanation / Answer

1) The attractive forces between molecules reduce the number of collisions with the container wall or with other molecule , this effect becomes more pronounced as the number of attractive interactions increases. Because the average distance between molecules decreases, the pressure exerted by the gas on the container wall decreases, and the observed pressure is less than usually expected .

2) The pressure term(P + (an2/V2) corrects for intermolecular attractive forces that tend to reduce the pressure from that predicted by the ideal gas law. Here, n2/V2 represents the concentration of the gas (n/V) squared because it takes two particles to engage in the pairwise intermolecular interactions of the type.

also a is a measure of the magnitude of the attractive forces among molecule of the gas and b is the measure of effective size of the gas molecule

3) units of a as p= an2/ V2 -> a= p*V2/n2 =atm L2 mol-2

units of v =nb -> b= v/n = L mol-1

4) at high temperature and at low pressure gases behave as a perfect gases because

The molecules of ideal gas dont exert force of attraction on each other. Moreover an ideal gas donot have finite volume. Under high temperature and low pressure, molecules of real gas move so apart from each other due to which the force of attraction between them becomes neglegible .

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