Hess Law and Enthalpy of Reaction

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TITLE: Hess Law and Enthalpy of Reaction
TASK DEVELOPER: Jane Silverstein
GRADE AND CONTENT AREA: Chemistry II AP 12th
SCOPE AND SEQUENCE: Chapter 17
TARGET TEACHING DATE: Mar. 30, 2007
SCHOOL: John F. Kennedy High School

STANDARDS:

CHEMISTRY - GRADES 9-12

STANDARD 5.6 CHEMISTRY: All students will gain an understanding of the structure and behavior of matter.

Strand B. Chemical Reactions: Building upon knowledge and skills gained in preceding grades, by the end of Grade 12, students will:

1. Explain that the rate of reactions among atoms and molecules depends on how often they encounter one another and that the rate is affected by nature of reactants, concentration, pressure, temperature, and the presence of a catalyst.

MATHEMATICAL APPLICATIONS

STANDARD 5.3 MATHEMATICAL APPLICATIONS: All students will integrate mathematics as a tool for problem-solving in science, and as a means of expressing and/or modeling scientific theories.

Strand B. Geometry and Measurement: Building upon knowledge and skills gained in preceding grades, by the end of Grade 12, students will:

1. When performing mathematical operations with measured quantities, express answers to reflect the degree of precision and accuracy of the input data.

Strand C. Patterns and Algebra: Building upon knowledge and skills gained in preceding grades, by the end of Grade 12, students will:

1. Apply mathematical models that describe physical phenomena to predict real world events.

PERFORMANCES:

In a laboratory setting, the students will measure the heats evolved in three different reactions. They will use Data capture software to measure, graph and present data. They will then calculate the heat evolved from one of the reactions, using standard values for the other two and compare experimental results with expected values.

SETTING:

Real World Setting: Laboratory applications

You are a research chemist. You are utilizing a process to measure heat evolved by a chemical process. You will first try the process on reactions with known values, to see how accurately the process works.

SMARTSKILLS:

Level I: Acquiring Data -

Skills: Using data capture software, temperature probes, calculations to determine the enthalpy of a reaction.
Concepts: Heat can only be measured when it causes a change in temperature or phase.
Processes: Measuring change in temperature over a period of time, mass, heat flow.

Level II: Visualizing Information -

Organizing: Data is graphed and tabulated.
Creating patterns: Data is used to predict unmeasured values.

Level III: Applying Knowledge -

Comparing the calculated results with predicted results.
Using error to evaluate experimental protocol.

PREFERENCES:

Student Involvement -

In a whole class setting - discuss definition of Enthalpy, difficulties measuring heat, heat capacity, possible sources of error.
As a cooperative group - Prepare solutions of desired Molarity needed for the experiment.

Instruction - Activities will be organized and delivered by students to learn from hands-on activities

Use of Resources - The school will provide laboratory equipment, materials

Use of Resources - The students will provide classroom materials such as pencils, paper, notebooks

Assessment of Student Work and Reporting Results - The following forms of assessment will be used to determine progress and results:

The students will present their work as a laboratory report, which they will prepare working in a small collaborative group. A rubric will be provided to ensure that all parts of the report are included.
Test for accuracy of work will be made in experimental investigations and calculations.
An assessment will be administered, to ensure that all students participate in the collaboration.

Timeline - The estimated time needed to plan, teach, and score this task is 5 days of group work and homework time to prepare report.

ACTIVITIES:

Chemistry Lab

PLANNING PHASE
Estimated Time: 1 hour

Review and align instructional assignment with standards, performances, and smart skills
Develop student assignments for the chemistry lab investigation that supports the concept being taught. Prepare materials for students to use in doing the experiment..
Provide an overview to students about expectations, activities, and assignments. Provide prelab assignment.

IN THE Chemistry LAB

Activity One: Reaction solid NaOH and water
Estimated Time: 40 minutes

Step 1: Set up data collection equipment, start software.
Step 2: Weigh solute
Step 3: Make solution using solute and distilled water. Measure and graph results.

Activity Two: Reaction solid NaOH and dilute HCl
Estimated Time: 40 min

Step 1: Set up data collection equipment, start software.
Step 2: Weigh solute
Step 3: Make solution using solute and HCl. Measure and graph results.

Activity Three:
Estimated Time: 40 minutes

Step 1: Set up data collection equipment, start software.
Step 2: Measure out both solutions, NaOH and HCl
Step 3: Mix solutions . Measure and graph results.

Activity Four:Estimated time: 40 minutes

Students will write a report of their laboratory activity. The report will include: Purpose, Procedure, Results, Data Analysis, Conclusion

RETURNING TO THE CLASSROOM

Step 1: Discuss sources of error, in process and in performance, as written in the conclusion to the lab report..
Step 2: Design another investigation that might minimize errors.

BENCHMARKING:

Student Performance One:Students will be able to measure change of temperature and calculate heat flow and enthalpy.

Student Performance Two: Students will write net ionic equations and calculate heat of reaction using Hess' Law.

Student Performance Three: Students will write a lab report.

SCORING:

Science Rubric: Constructed Response Items

Kennedy High School Science Rubric: Laboratory activity
Level 4	There is evidence in this response that the student has a full and complete understanding of the investigation.. Purpose and procedure are not copies of directions Data is presented clearly, tables are labeled Data analysis is complete and accurate Calculations are correctly done Errors are less than 5% Conclusion is complete, errors are discussed
Level 3	There is evidence in this response that the student has a good understanding of the question or problem. Purpose and procedure are not copies of directions Data is presented clearly, tables are labeled Data analysis is complete and accurate Calculations are correctly done Errors are less than 10% Conclusion is incomplete, errors are discussed, but not carefully though out.
Level 2	There is evidence in this response that the student has a basic understanding of the question or problem. Purpose and procedure are copies of directions Data is presented clearly, tables are labeled Data analysis is incomplete and inaccurate Calculations are correctly done Errors are less than 15% Conclusion is incomplete, errors are discussed superficially
Level 1	There is evidence in this response that the student has some understanding of the question or problem. Purpose and procedure are copies of directions Data is not presented clearly, tables are not labeled Data analysis is incomplete and/ not done Calculations are incorrectly done or absent Errors are greater than 15% Conclusion is incomplete, errors are not discussed
Level 0	There is evidence that the student has no understanding of the question or problem. The response is completely incorrect or irrelevant or there is no response.

METACOGNITION:

Cognitive Information: I will collect the following information:

After the laboratory activity, students will discuss sources of error in calculation and in experimental protocol.
Laboratory report will be scored according to the rubric.

RESULTS:

Organize: I will use the following chart to display student data for each time that I assess and score the same learning standard(s):

Data-Driven Results Disaggregated by Gender and All Students

Content Standard: STANDARD 5.6 CHEMISTRY: All students will gain an understanding of the structure and behavior of matter. Strand B. Chemical Reactions: Building upon knowledge and skills gained in preceding grades, by the end of Grade 12, students will: 1. Explain that the rate of reactions among atoms and molecules depends on how often they encounter one another and that the rate is affected by nature of reactants, concentration, pressure, temperature, and the presence of a catalyst.
Students	Scoring Results
Last Name and First Name	Male	Female	All Students
1.		4	4
2.	4		4
3.		4	4
4.	4		4
5.	4		4
6.		4	4
7.		4	4
8.	4		4
9.	4		4
10.		4	4
11.	4		4
12.		4	4
# Of students at the Advanced Performance Level			12

Analyze: Contributing factors - These students are taking their second year of Chemistry Lab. They are all exceedingly proficient and it would be surprising if they were not successful at completing this activity.

Reflect: This concept has always been a difficult one, and it took an additional day, beyond those anticipated, to discuss the application of Hess' law and the measurement of heat. One of the major problems is to have students understand the difference between the calculations used to measure heat and the enthalpy calculations used to find additional enthalpies. The results indicate that this group did understand the difference.

Summarize: This activity was successful. I think I shall try to incorporate it into the first year of Chemistry next year, rather than wait for AP Chemistry. Perhaps it will help them avoid some of the confusion that arises when we discuss heat, heat flow and enthalpy.

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