Please complete this assignment before the next class meeting. Written answers t
ID: 979952 • Letter: P
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Please complete this assignment before the next class meeting. Written answers to questions must be handed in at the beginning of class. I. Read sections 2.5, 2.9 and 2.10 in the textbook. II. 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 sections in the textbook specified in part I 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. Why do calorimeters need to be calibrated? 2. In one of the General Chemistry experiments, you used a coffee-cup calorimeter to measure the heat of neutralization of selected acid-base reactions. The calorimeter consisted of two nested Styrofoam cups with a cardboard lid. A temperature probe was lowered in the solution through a hole in the lid. a) Is a coffee-cup calorimeter a constant-volume device? b) ls a coffee-cup calorimeter a constant-pressure device? c) Is a coffee-cup calorimeter adiabatic? d) Would a coffee-cup calorimeter need to be calibrated? If so, suggest an appropriate procedure. As a result of the experiment, you calculated q CAT for the neutralization reactions. e) In that case, was q equal to AU or AH? 3. Explain why molar heat capacity is an intensive property. Is specific heat capacity an intensive property?Explanation / Answer
ANSWER
2. (a) Yes a coffee-cup calorimeter is a constant volume device. Since the coffee-cup is closed with a lid the volume of gets resticted to the volume of coffee-cup
(b) Coffee-cup calorimeter is not a constant pressure device.
(c) Coffee-cup calorimeter is adiabatic device since the walls of coffee-cup are bad conductors of heat.
(d) Yes coffee-cup calorimeter needs to be calibrated since there are chances of small heat exchange.
we can measure heat of a reaction in a coffee-cup calorimeter and the compare it with the standard value of heat of reaction and note the difference.
(e) In this case q is equal to U. because measurement is done at constant volume hence we can use Cv and not Cp. U = CvT
(3) Heat capacity is an EXTENSIVE property as its value varies with mass. But if we fix the amount of maas it bcomes INTENSIVE PROPERTY. That is why molar specific heat is intensive property as the mass is fixed to one mole of substance. Specific heat capacity is also ann INTENSIVE property becaue the mass is fixed as 1g.
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