THC_Thermochemistry Module Overview

Thermochemistry Module Overview

Introduction

In this module you will learn the relationship between energy and chemical reactions. You will learn the difference between energy, heat, and work, perform calorimetry calculations, and study the laws of thermodynamics, enthalpy, entropy, and Gibbs free energy. All changes in matter involve some form of energy change. Thus, the availability or disposition of energy plays a role in virtually all observed chemical processes. Thermodynamics provides a number of tools for understanding this key role, particularly the conservation of energy, including energy transfer in the forms of heat and work.

Module Lessons Preview

• How do you convert temperatures from Fahrenheit to Celsius to Kelvin?
• What is the difference between kinetic and potential energy?
• How does kinetic energy vary with temperature?
• How is energy involved in forming and breaking bonds?
• What are the system, surroundings, boundary, and insulated system?
• How is enthalpy affected by its sign?
• What is a state function?
• How is overall enthalpy determined from an enthalpy diagram?
• How is Hess' Law used to determine a reaction's enthalpy?
• What are the Three Laws of Thermodynamics?
• What is the relationship between heat, work, and energy change?
• What is entropy?
• How can the sign of ∆S and ∆H be predicted?
• What is Gibbs Free Energy and how does it relate to enthalpy and entropy?
• How is temperature determined for a phase change when enthalpy change and entropy change are known?

Key Terms

1. Bond Energy - Bond energy is the amount of energy required to break apart of mole of molecules into component atoms
2. Boundary - that which divides a system from its boundaries
3. Calorie (Cal) - 4.184 J. The energy that will raise the temperature of 1.00 g of water from 14.5 to 15.5°C
4. Calorimeter - an apparatus used in the determination of the heat of a reaction
5. Change in entropy, ΔS - for a change, the sum of the values of S for the products minus the sum of the values of S for the reactants
6. Chemical Energy - the potential energy of chemicals that is transferred during chemical reactions
7. Closed System - a system that is not open to the atmosphere, allowing only energy to cross the boundary
8. Endothermic - a process or reaction in which the system absorbs energy from its surroundings in the form of heat
9. Enthalpy change, Δh - the difference in enthalpy between the initial state and the final state for some change
10. Enthalpy, H - the heat content of a system
11. Entropy - the thermodynamic quantity that describes the degree of randomness of a system. The greater the disorder or randomness, the higher is the statistical probability of the state and the higher is the entropy
12. Exothermic - a process or reaction in which the system releases energy to its surroundings in the form of heat
13. First Law of Thermodynamics - a formal statement of the law of conservation of energy
14. Gibbs free energy, G - a thermodynamic quantity that relates enthalpy (H), entropy (S), and temperature (T) by the equation, G = H - TS
15. Heat - the transfer of thermal energy
16. Heat Capacity - the quantity of heat needed to raise the temperature of an object by 1°C
17. Hess's Law - for any reaction that can be written in steps, the standard heat of reaction is the same as the sum of teh standard heats of reaction for the steps
18. Internal Energy, E - the sum of all the kinetic energies and potential energies of the particles within a system
19. Isolated System - a system that permits no matter or energy to pass through
20. Joule - the SI unit of energy; 1 J = 1 kh m2 s-2
21. Molar Heat of Fusion  - the heat absorbed when 1 mol of solid melts to give 1 mol of the liquid at constant temperature and pressure
22. Molar heat of vaporization - the heat absorbed when 1 mole of a liquid changes to 1 mol of its vapor at constant temperature and pressure
23. Open System - a system that is open to the atmosphere, allowing energy and matter to cross the boundary
24. Second Law of Thermodynamics - whenever a spontaneous event takes place, it is accompanied by an increase in the entropy of the universe
25. Specific Heat Capacity - the quantity of heat that will raise the temperature of 1 g of a substance by 1°C
26. Spontaneous Change - a change that occurs by itself without outside assistant
27. Standard Enthalpy of Formation - the amount of heat absorbed or evolved when one mol of the compound is formed from its elements in their standard states
28. Standard Heat of Reaction - the enthalpy change of a reaction when determined with reactants and products at 25°C and 1 atm and on the scale of the mol quantities given by the coefficients of the balanced equation
29. Standard State - the condition in which a substance is in its most stable form at 25°C and 1 atm
30. Surroundings - the part of the universe other than the system being studied and separated from the system by a real or imaginary boundary
31. System - that part of the universe under study and separated from the surroundings by a real or an imaginary boundary
32. Temperature - a measure of the hotness or coldness of something and proportional to the average molecular kinetic energy of the atoms, molecules, or ions present
33. Thermochemical Equation - a balanced chemical equation accompanied by the value of ΔH° that corresponds to the mol quantities specified by the coefficients.
34. Thermodynamics - the study of the laws that govern the energy and entropy changes of physical and chemical events
35. Third Law of Thermodynamics - for a pure crystalline substance at 0 K, S = 0
36. Work - the energy expended in moving an opposing force through some particular distance

eTextbook Reminder

As you read these content pages, also read the corresponding content in your etextbook. Work the example problems in the text as you read to make sure that you understand. The etextbook sections will be listed with the corresponding content pages on your schedule.  

Thermochemistry Practice Problems

Before you begin, print the module practice problems found below.  You should complete a section of problems after covering that particular portion of the content. 

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