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Chem Chapters 7-9 Cheat Sheet (DRAFT) by

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This is a draft cheat sheet. It is a work in progress and is not finished yet.

7.1

Evidence of a Chemical Reaction
Types of Chemical Reactions
Change in Color
Combin­ation: A+ B -> AB
Formation of Gas (bubbles)
Decomp­osi­tion: AB -> A + B
Heat (or a flame) Produced or absorbed
Single Replac­ement: A + BC -> AC + B
Formation of a Solid (preci­pitate)
Double Replac­ement: AB+CD -> AD + CB
 
Combus­tion: a carbon containing compound burns in oxygen gas to produce the gases carbon dioxide (C02), water (H20), and energy in the form of heat or a flame

7.1

Formation of Gas
Evidence of a Chemical Reaction
1 Change in Color

7.10 Energy in Chemical Reactions

Energy Units
1 kilojoule (kJ) = 1000 joules (J)
 
used to show the energy change in a reaction
Heat of Reaction: the amount of heat absorbed or released during a reaction that takes place at a constant pressure.
ΔH= H(prod­ucts) - H(reac­tants)
Exothermic Reaction: energy is released
HEAT IS WRITTEN AS A PRODUCT
 
-ΔH
 
the energy of the products is lower than the reactants
Endoth­ermic Reaction: heat is absorbed
HEAT IS WRITTEN AS A REACTANT
 
+ΔH
 
the energy of the products is higher than the reactants

7.10 Energy in Chemical Reactions

Energy Units
1 kilojoule (kJ) = 1000 joules (J)
 
used to show the energy change in a reaction
 

Charac­ter­istics of Oxidation and Reduction

Always Involves
May Involve
Oxidation
Loss of electrons
Addition of oxygen
 
Loss of hydrogen
Reduction
Gain of electrons
Loss of oxygen
 
Gain of hydrogen

Percent Yield

Percent yield (%) =
actual yield/­the­ore­tical yield x100%
Theore­tical Yield: expected value (calcu­lated)
Actual Yield: Measured value (mass of the product) (given value)
 
less than the theore­tical yield
How do you find the percent yield of a reaction?
Step 1:State given and needed quantities
 
Step 2: Use coeffi­cients to write mole-mole factors; write molar mass factors.
 
Step 3: Calculate the percent yield by dividing the actual yield (given) by the theore­tical yield and multip­lying the result by 100%.

Gas

Air is a mixture of
78% Nitrogen gas, and 21% Oxygen gas, argon, carbon dioxide, and water vapor
Kinetic Molecular Theory of Gases
helps us understand gas behavior
1. A gas consists of small particles (atoms or molecules) that move randomly with high velocities
Gas molecules moving in random directions at high speeds cause a gas to fill the entire volume of a container.
2. The attractive forces between the particles of a gas are usually very small.
Gas particles are far apart and fill a container of any size and shape.
3. The actual volume occupied by gas molecules is extremely small compared to the volume that the gas occupies.
The volume of the gas is considered equal to the volume of the container. Most of the volume of a gas is empty space, which allows gases to be easily compre­ssed.
4. Gas particles are in constant motion, moving rapidly in straight paths.
When gas particles collide, they rebound and travel in new direct­ions. Every time they hit the walls of the container, they exert pressure. An increase in the number or force of collisions against the walls of the container causes an increase in the pressure of the gas.
5. The average kinetic energy of gas molecules is propor­tional to the Kelvin temper­ature.
Gas particles move faster as the temper­ature increases. At higher temper­atures, gas particles hit the walls of the container more often and with more force, producing higher pressures.
Atmosp­heric Pressure
higher altitudes = less pressure
Units for Pressure (P)
atmosphere (atm)
 
millim­eters of mercury (mmHg)
 
torr (Torr)
 
pascal (Pa)
Units for Volume (V)
liters (L)
Units for Temper­ature (T)
kelvin (K)
 
K= 273 + ° C
Units for amount of Gas (n)
gram (g)
 
mole (n)
Measur­ement of Gas Pressure
P= force/area
1 atm = 760 mmHg = 760 Torr (exact)
1 atm = 29.9 inHg
1 mmHg = 1 Torr (exact)
1atm = 101,325 Pa = 101.325 kPa
1 atm = 14.7 lb/in2 (psi)
**Boy
 

The Mole

Avogadros Number: 6.02 x 1023
atoms or particles of that element
 
number of moles will be a smaller number
The chemical formula subscripts specify the:
Atoms in 1 molecule
 
Moles of each element in 1 mole
How do you calculate the moles of an element in a compound?
Step 1: State the given and needed quantities
 
Step 2: Write a plan to convert moles of a compound to moles of an element.
 
Step 3: Write the equalities and conversion factors using subscr­ipts.
 
Step 4: Set up the problem to calculate the moles of an element.
Molar Mass: The quantity in grams that equals the atomic mass of that element
1 mole of C = 12.01g = 6.02x1023 atoms of C obtained from the periodic table
How do you find the molar mass of a compound?
Multiply the molar mass of each element by its subscript in the formula and add the results
Calcul­ations using molar mass
Molar mass converts moles of a substance to grams, or grams to moles.

Limiting Reacta­nts

Limiting Reactant
the reactant that is completely used up
 
the reactant that does not completely react and is left over is called the excess reactant
How do you find out what is the limiting reactant and how many moles (or grams) of products can be produced?
Step 1: State the given and needed quantities (moles).
 
Step 2: Use coeffi­cients to write mole-mole factors
 
Step 3: Calculate the quantity (moles) of product from each reactant, and select the smaller quantity (moles) as the limiting reactant.