Need help with UMUC NSCI 101/103 Chemical Processes UMUC NSCI 101/103 Lab 5: Che

Question

Need help with UMUC NSCI 101/103 Chemical Processes

UMUC NSCI 101/103

Lab 5: Chemical Processes

INSTRUCTIONS:

·On your own and without assistance, complete this Lab 5 Answer Form and submit it via the Assignments Folder by the date listed on your Course Schedule (under Syllabus).

·To conduct your laboratory exercises, use the Laboratory Manual that is available in the classroom. Laboratory exercises on your CD may not be updated.

·Save your Lab 5 Answer Form in the following format: LastName_Lab5 (e.g., Smith_Lab5).

·Submit your document in a Word (.doc or .docx) or Rich Text Format (.rtf) for best compatibility.

Pre-lab Questions

Define enthalpy.

What is the relationship between the enthalpy of a reaction and its classification as endothermic or exothermic?

With instant hot compresses, calcium chloride dissolves in water and the temperature of the mixture increases. Is this an endothermic or exothermic process?

Table 2: Hand Warmer Data

Table 1: Cold Pack Data

Experiment 1: Cold Packs vs. Hand Warmers

Time (sec)

Temp. (°C)

Initial

30

60

90

120

150

180

210

240

270

*300

330

360

390

420

450

Maximum Temp (°C):

Time (sec)

Temp. (°C)

Initial

30

60

90

120

150

180

210

240

270

*300

330

360

390

420

450

Minimum Temp (°C):

Graph your data from the tables. You may create the graph on any program, but make sure it can be integrated into this document.

Questions

1.Calculate the overall temperature change for the cold and hot pack substance. HINT: This is the difference in the maximum temperature and minimum temperature of each.

Cold pack T:                    

Hand warmer T:            

Which pack works by an exothermic process? Use experimental data to support your answer.

Which pack works by an endothermic process? Use experimental data to support your answer.

Which pack had the greatest change in enthalpy? How do you know?

Table 2: Hand Warmer Data

Explanation / Answer

You have not given the experimental data so I can answer only the first part of the question.

1. Definition of enthalpy: Enthalpy(H) is a thermodynamic quantity which describes the total heat content of the reaction. It cannot be measured but the change of enthalpy (dH) is a process can be measured.

2. Relationship between the enthalpy of a reaction and its classification as endothermic or exothermic:

Consider a reaction/process: A + B ==> C               ;dH = change of enthalpy = Hfinal - Hinitial

If dH for the process is negative, it is called an endothermic process, as heat is absorbed during the course of the reaction.

If dH for the process is positive, it is called an exothermic process, as heat is evolved during the course of the reaction.

3. CaCl2 + water ==> solution      

Here, dH= positive, as temperature of the mixture increases so we can say that heat is evolved in this process. This is an exothermic process.

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