Cheatography
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Balancing Equations
Stoichiometry
Formula Determination
Limiting Reagents
This is a draft cheat sheet. It is a work in progress and is not finished yet.
Terminology
Reactants |
substances consumed during a chemical reaction |
Products |
substances formed as a result of a chemical reaction |
Chemical Equation |
a description of the identities and proportions of the reactants and the products in a chemical reaction |
Balanced Chemical Equation |
total number of atoms of each element are the same on the right and left side of the reaction arrow |
Law of Conservation of Mass |
the principle that the sum of the masses in a chemical reaction is equal to the sum of the masses of the products |
Stoichiometry |
the study of the numerical relationship between chemical quantities in a chemical reaction |
Phase Symbols |
represent physical states of reactants and products: (g) gases, (l) liquids, (s) solids, (aq) aqueous solution |
7.2 Writing Balanced Chemical Equations
Chemical Equations relate the quantities of substances consumed and produced in chemical reactions |
Concepts of Mole & Molar Mass describe macroscopic quantities of substances in terms of the number of particles they contain |
Combination Reaction a reaction in which two or more substances form a single product |
Combustion Reactions a rapid reaction between fuel and oxygen that produces and releases energy |
Lack of any coefficients indicates that one atom of something reacts with a single atom of something else to produce one molecule of product |
C(s) + O2(g) -> CO2(g) |
+ -> |
Any number of moles (X moles) can react with an equal number of moles of another reactant (Y moles) to produce the same quantity of product (XY moles) |
7.2 Describing Chemical Reactions
S(s) + O2(g) -> SO2(g) |
+ -> |
4 Ways to Describe Chemical Reactions |
1) One atom of sulfur reacts with one molecule of oxygen to produce one molecule of sulfur dioxide |
2) The coefficients tell us that one mole of sulfur reacts with one mole of oxygen to produce one mole of sulfur dioxide |
3) Avogadro's constant describes that 6.022 x 1023 atoms of sulfur react with 6.022 x 1023 molecules of oxygen forming 6.022 x 1023 molecules of sulfur dioxide |
4) The Molar Masses of the reactants and products allow us to say that 32.06 grams of sulfur react with 32.00 grams of oxygen to produce 64.06 grams of sulfur dioxide |
General Rules for Balancing Equations
First attempts at balancing equations may not work. Try a different approach starting with a different element. |
Balance pure elements last (O2, H2, N2) |
Do not break up polyatomic ions (SO42-) |
4-Step Method for Writing Balanced Equations
Element |
Sulfur |
1) Write a preliminary expression containing a single particle (atom, molecule, or formula unit) of each reactant and product with a reaction arrow separating reactants from products. Include phase symbols indicating physical states. |
SO2(g) + O2(g) -> SO3(g) |
2) Check whether the expression is balanced by counting the atoms of each element on each side of the reaction arrow. |
Reactant Side |
1 |
Product Side |
1 |
Balanced? |
yes |
Element |
Oxygen |
Reactant Side |
2+2 = 4 |
Product Side |
3 |
Balanced? |
no |
3) Choose an element that appears in only one reactant and one product and balance it first. |
The only element that occurs only once on each side of the reaction arrow in this equation is sulfur, but it is already balanced, so this step can be skipped. |
4) Choose coefficients for the other substances os that the number of atoms for each element is the same on both sides of the reaction arrow. |
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Reaction Stoichiometry
Ratio of Coefficients in a Chemical Reaction (Mole Ratio) |
* specify the relative amounts in molecules or moles of each of the substances involved in the reaction |
* act as a conversion factor between the amount in moles/molecules of the reactants and products |
* can be used to determine how much of one reactant is needed to completely react with another quantity of the other reactant |
Example Ratio of Coefficients
if 22.0 moles of C8H18 are burned, how many moles of CO2 form? |
Stoichiometric Ratio |
22.0 mol C8H18 x 16 mol CO2/2 mol C8H18 = 176 mol CO2 |
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