Chemistry ClassesReview for Unit Exam

Friday June 7, 2013

Format

• Approximately 20 questions• Multiple Choice• Scantron (bring #2 pencils)• You may use an index card of information as a

reference

Topics

• Types of reactions• Balancing Equations• Conversions and conversion factors• Stoichiometry• Percent Yield

Definitions

• Know the following:– Reactants and Products– Law of Conservation of Matter– Molar Mass– Stoichiometry– Balanced Equations– Types of Reactions (for Mr. Basa’s classes)

Types of reactions

• Synthesis:

• Decomposition:

• Single Replacement:

• Double Replacement:

• Combustion:

Conversions (practice problems)

• 1. How many atoms are there in a mole of helium? • 2. How many molecules are there in a mole of

methane? • 3. What is the mass of 1 mole of magnesium? • 4. What is the mass of 2 moles of carbon dioxide? • 5. How many atoms are there in 27.9 grams of iron?

Balancing equations

• Remember:– Count # of atoms for reactants and # of atoms for

products (i.e., on both sides of the arrow)– If not equal, place a number on the coefficient line

(nowhere else!) to multiply times the # of atoms for that compound, and recount

– If still not equal, change the coefficient and repeat the above

Practice problems

Stoichiometry

• The goal is to have use the number of moles of each compound in a reaction to answer questions about that reaction.

• Write down the given information• Understand what the question is asking for• Make a “model” to solve the question

(continued)

Stoich, cont.

• Example of model:gram mole mole gram

• The 1st pair of parentheses (what needs to be converted) will always be the given

• The 3rd pair of parentheses will usually be the molar ratio

• The last pair of parenthesis will be what you are trying to solve for

Practice problems

Percent Yield

• Easier than you think! : )• Determine what the theoretical yield is (might

use stoich to solve)• Record your actual yield• Percent Yield = actual yield X 100

theoretical yield

Practical hints

• Work quickly (i.e., use time wisely: know when it’s the half way point of the class, etc.)

• Answer questions you know right away and come back to the more challenging questions

• For your choices, eliminate distractor choices• Study hard each night before the test – divide

the topics so you don’t “cram” all at once• Good luck!