Homework

# Thermodynamics in Chemistry

## Chapter 5: 4-5 Homework

Textbook assignment: Read Kotz and Triechel, Chemistry and Chemical Reactivity Chapter 5 Sections 4 to 5.

##### Study Notes

5.4 Changes in energy content take two forms: heat flow and work. We measure work by movement, remember. Work done on by a system on its environment means that the system must expand into the environment; work done on the system by the environment means the environment pushes on the system. We measure this as a change in volume. If volume doesn't change (usually the case in most solution reactions), then all energy changes are heat flows into or out of the system.

5.5 Be sure that you understand what enthalpy is: the amount of heat energy stored in a system. Like potential energy in gravity systems, we always measure this as a change from some base position and express it as a function of the amount of matter involved. Heat LOSS is expressed as a negative amount. ΔH = -243kJ means that heat was released by the reaction.

### Important Equations and Conversion Factors

EquationNotes
ΔU = q + w U is the change in energy of the system as a result of
heat flow q into or out of the system and
work w done on (positive) or by the system (negative)
w = -P ΔV
where w = work done at constant pressure P
while volume changes ΔV = Vfinal - Vinitial
H = U + PV
H is the instantaneous total energy or enthalpy of the system
ΔH = ΔU + PΔV
[where P is held constant]

In solutions, ΔV = 0, so ΔH = ΔU: it is equal to the heat flow into or out of the chemical system.

#### Web Lecture

Read the following weblecture before chat: Heat Capacity

#### Videos for Chapter 5: Energy and Chemical Equations

Review the Videos at Thinkwell Video Lessons under THERMOCHEMISTRY.

• Constant Pressure Calorimetry
• Bomb Calorimetry (Constant Volume)
• Heats of Reaction

Use the Coffee Problem at the Chem Collective to make the perfect cup of coffee by using your knowledge of heat capacity. Follow the instructions in the lab bench simulation (you'll need these techniques for the next assignment).

#### Chat Preparation Activities

• Essay question: The Moodle forum for the session will assign a specific study question for you to prepare for chat. You need to read this question and post your answer before chat starts for this session.
• Mastery Exercise: The Moodle Mastery exercise for the chapter will contain sections related to our chat topic. Try to complete these before the chat starts, so that you can ask questions.

#### Chapter Quiz

• There is no chapter quiz YET.

#### LAB #3 GUIDED INQUIRY: Measuring the enthalpy of reaction-- Phase II

Use your calorimeter to determine the specific heat of a metal.

References:

• IGHCE Lab 15.1-2 OR HSCKM IX-1-2 Determine the Heat of Solution and Heat of Fusion
• IGHCE Lab 15.3 OR HSCKM IX-3 Determine the Specific Heat of a Metal
• IGHCE Lab 15.4 OR HSCKM IX-4 Determine the Enthalpy Change of a Reaction
• AP2009 #13 - Determination of Enthalpy Change Associated with a Reaction â€¢APGIE Investigation 12: The Hand Warmer Challenge: Where does the Heat Come From?
• Alternative lab: Calorimetry and Specific Heat