CHEMISTRY 103-Lab Exam 4-with 100% verified answers-2024-2025.docx, Exams of Chemistry

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CHEMISTRY 103-Lab Exam 4-with

100% verified answers-2024-

● Due No due date ● Points 30 ● Questions 3 ● Time Limit 60 Minutes

Attempt History

Attempt Time Score LATEST Attempt 1 58 minutes 23 out of 30 Score for this quiz: 23 out of 30 Submitted Sep 15 at 11:31am This attempt took 58 minutes. Question 1 10 / 10 pts

1. (3 points) What does it mean that the heat of a reaction is an extensive property?
2. (3 points) Does the following reaction give off heat or absorb heat? Explain briefly. C D H = +263Kcal/mol
3. (4 points) In one experiment in the video, room temperature water was mixed with water at about 38 degrees. To what temperature (about) did the mixture of the two water samples come to after setting for a few minutes? Your Answer: 1. Extensive properties can be mass or volume, depend on the amount of matter being measured 2. Endothermic absorbs heat because delta H Positive 3. 29.8 C

1. The heat depends on the amount of substance. If the amount of substance is doubled, then

the heat doubles. Other properties, such as density, are intensive, which means the amount of substance does not matter.

2. The (+) value indicates this reaction absorbs heat.
3. The mixture reached 30 oC, but settled to 29.8oC. Question 2 5 / 10 pts
4. (3 points) A student conducted an experiment where he mixed 75 g of tap water (25.0oC) with 75g of warm water(35.0oC). The final temperature of the mixture was 28.0oC. How much heat was lost by the warm water if the specific heat of water is 4.18 J/K-g?
5. (3 points) In one experiment in the video, NaOH was mixed with another substance. What other substance was mixed with NaOH?
6. (4 points) One student conducts an acid-base reaction where she finds the following results. What is the enthalpy of the reaction (in KJ/mol)? Heat gained by solution 4215 J Heat gained by calorimeter 256 J Moles of product formed 0. mol Your Answer:
7. 75 x 4.18 x 10 3,135 kj

HCL

H1: 4215

• H2 :

4215+ 256= 4471j enthalpy of the reaction/ mole of product -4471 j/ 0.26 mol = -16620. j/mol = enthalpy of reaction = - 16.62 kj/mol

2. HCl (hydrochloric acid)

3. 16.62 KJ/mol or 16.6 KJ/mol Total heat = Solution heat + Calorimeter heat (total heat produced) Total heat = 4215 J + 256 J = 4471J or 4.471 KJ Enthalpy of reaction = Total heat gained/moles of product Enthalpy of reaction = 4.471 KJ/0.269 mol = 16.62 KJ/mol #1 is incorrect. #2 is HCl, not HCL #3 is positive. Question 3 8 / 10 pts

4. (3 points) How much water was heated in the combustion part of the experiment?

2. (3 points) The accepted fuel value for a substance is 6020 cal/g. If a student determines the value to be 1256 cal/g, then what is the percent efficiency of the experiment.

3. (4 points) The combustion experiment did not adequately measure the fuel value (low efficiency). What are some ways to increase the efficiency of the experiment? Your Answer: 500 ML actual/ theoretical accepted x 100% 1256 cal/g / 6020 x 100%= 20.9% use a better isolation container, better heat measuring device, better heating source .
4. 500 g or 500 mL
5. The experimental setup relied on heat being transferred from the heat to the water. However, much of the heat (65%) was lost to the air, while the rest was lost to the calorimeter, and ring stand. Hence, using a better insulator to prevent the heat from escaping into the air or using an insulated lid (not cardboard) to prevent heat loss would help. The heat lost to the air was the biggest culprit.

Quiz Score: 23 out of 30