Homework

# Chemical Equations and Chemical Equilibrium

## Chapter 3: 1-3 Homework

Textbook assignment: Read Kotz and Triechel, Chemistry and Chemical Reactivity Chapter 3: Sections 1 to 3.

##### Study Notes

3.1: Chemical Equations Because atoms are unbreakable for the purposes of chemical reactions, we must of reactions as involving the rearrangements of whole atoms or groups of atoms. Because mass is conserved, no atoms are ever created or destroyed in a chemical reaction, so the number of each elemental type of whole atoms must be the same before and after the reaction occurs. This allows us to determine the actual number of atoms involved from partial information.

3.2: Balancing Chemical Equations The first step of balancing a reaction is to determine which chemicals are involved. Then we adjust coefficients (the number of whole atoms or molecules in a unit), Study the process on p. 152 carefully. We leave until last balancing the one element that stands alone, since that piece we can manipulate without affecting anything else. For combustion reactions, this is the oxygen.

3.3: Chemical Equilibrium. Chemical reactions occur between individual molecules. The amount of energy available at the point of a reaction determines which set of molecules breaks open to rearrage atoms in a different set. At any given moment, rearrangements may proceed in both directions. The overall effect depends on how many reactions occur in each direction. If most reactions at the molecular level favor production of a particular set of molecules, we consider these the products of the overall reaction and say the reaction is product-favored. If we start with one set of molecules and only a few react to form new sets, we say the reaction is reactant-favored.

#### Balancing Chemical Equations

StepsProcessExample
1Write out the reaction
description
Methane and oxygen react to form water and carbon dioxide.
2Substitute formulae for
reactants and products
CH4 + O2 → CO2 + H2O
3Since O2 is by itself, leave it until last. Balance carbon first.There is one C in products, one in reactants; carbon is balanced.
4Next balance hydrogenThere are four hydrogens in CH4; we need two water molecules so that we will have four hydrogen atoms in the products:
CH4 + O2 → CO2 + 2H2O
5Now balance oxygen.There are three oxygens in the products, so we need 3/2 diatomic oxygen for each methan molecule:
CH4 + 3/2 O2 → CO2 + 2H2O
6Double the reaction to get rid of the fraction, if desired2CH4 + 3O2 → 2CO2 + 4H2O
7Verify counts in reactants and productsCarbon: 2
Oxygen: 6
Hydrogen: 8
8Declare victory!Equation is balanced/

#### Web Lecture

Read the following weblecture before chat: Chemical Reactions

#### Videos for Chapter 3: Chemical Equations

Review the Videos at Thinkwell Video Lessons under REACTIONS IN AQUEOUS SOLUTIONS.

• Properties of Solutions
• The Electric Pickle

Use the simulation below to practice balancing equations.

• Open the introduction to learn how to manipulate the fields.
• To make ammonia, how many nitrogen gas atoms do you need? How many hydrogen gas atoms? How many ammonium molecules do you get? (When you've balanced the equation, you'll get a smiley face!) You can use the balance tool or the bar tool to help you visualize the proportions of elements.
• Balance the equation to separate water into its components.
• Balance the equation for burning methane in oxygen.
• Play the game. Can you succeed in balancing equations at level 3?

#### 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 Work

Labs for this skill set emphasize solution preparation techniques. Working with your teacher and teammates, design a lab to create several solutions of specific molarity/ molality that you can use in later experiments. Select up to three solutions, calculate the mass or volume of the solven and solute required for each, then demonstrate safety practices in solution preparation and storage.

References: Illustrated Guide to Home Chemistry Experiments [Required text], or Home School Chemistry Kit Manual which comes with the Home Scientist Chemistry Kit CK101 set and is available online at The Home Scientist.

• IGHCE Lab 7.1-2 Make up a molar / molal solution of a solid chemical
• IGHCE Lab 7.3 Make up a molar solution of a liquid chemical
• IGHCE Lab 7.4 Make up a mass-to-volume percentage solution