Scientific Understanding

This is one of the most difficult lessons for most students. Make sure you put a lot of effort into this lesson.

**NOTE:** None of the thermochemical numbers for the **Δ** H of chemical equations are true (EXCEPT NUMBERS ON OR THAT COME FROM THE **Δ** H or **Δ** G or **Δ** S TABLES). Also when I say that a certain equation is endothermic or exothermic I assigned these distinctions to demonstrate an example. I never actually looked them up in a book to see if they were true to the chemical process you would see in a laboratory. The fact that I made them up does not make any of my methods for solving these examples incorrect. Just don’t take the number you see here to be absolute truth. All of the numbers are created to guide you through the process of how to solve these problems.

**What is the lesson about?**

This lesson is about how we define and use energy in chemical equations. It also gives descriptions on how to more abstract concepts like entropy, spontaneity, work, and how energy relates to things like pressure, work, and volume.

**Why is it critical to understand?**

Once you know about the concepts of energy surrounding an equation you can make predictions about how efficient a chemical reaction would be. The energy of the equations is also the building block to understand how quickly a chemical reaction will take place. Although the speed of a chemical will not be discussed directly until the Reaction Rates Lesson, many of the measurements on how to read reaction rate graphs are first discussed in this lesson. The real world applications of Thermodynamics include tasks like at what temperature should you cook meat to kill bacteria. You could also do calculations on how much energy is required to travel with your car over a certain distance and link that back to how much fuel you will need to carry.

**What should you know before attempting this lesson?**

If you have trouble in this lesson go back to sections on

**New Learning Sections: **

—> Converting Between Joules and Calories

—> How Energy is Represented in a Chemical Equation **Part 1**

—> How to Calculate Enthalpy (Delta H) **Part 3**

—> Hess’ Law

—> Specific Heat Capacity **Part 1**

—> Heat of Fusion and Heat of Vaporization **Part 2**

—> Entropy Definition and Relationship to Energy **Part 1**

—> Entropy and States of Matter **Part 2**

—> Calulating Δ n (Delta n) **Part 3**

—> Spontaneous / Spontaneity Definition

—> **College:** Calculating Delta G (first way)

—> Calculating Delta G (second way)

**Reference Pages: **

**Worksheets: **