CHEM 4AA3 Chapter Notes - Chapter 4: Triethylene Glycol, Chemical Equation, Nitric Oxide

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Published on 19 Apr 2013
School
McMaster University
Department
Chemistry
Course
CHEM 4AA3
Professor
Chemistry Chapter Four
Chemical Reactions and Chemical Equations
A chemical reaction is a process in which one set of substances (reactants) is
converted to a new set of substances (products). The main evidences that prove
that a chemical reaction has occurred are:
a) Colour change
b) Formation of a solid (precipitate) within a clear solution
c) Evolution of a gas
d) Evolution or absorption of heat
To write the shorthand representation of a chemical equation certain steps must be
followed. Consider the chemical reaction: nitrogen monoxide + oxygen nitrogen
dioxide
1. Write the reaction using chemical symbols
NO + O2 NO2
2. Balance the chemical equation
2NO + 1O2 2 NO2
*** Balancing equations***
Remember these rules when balancing an equation
1. An equation can be balanced only by adjusting the coefficients of formulas.
2. Never introduce extraneous atoms to balance.
NO + O2 NO2 + O
3. Never change a formula for the purpose of balancing an equation.
NO + O2 NO3
When balancing equations, using these strategies will result in efficient balancing of
chemical equations.
Balance elements that occur in only one compound of each side first.
Balance free elements last.
Balance unchanged polyatomics (or other groups of atoms) as groups.
Fractional coefficients are acceptable and can be cleared at the end by
multiplication.
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Problem: Balance C6H14O4 + O2 CO2 + H2O
Solution:
Balance C: C6H14O4 + O2 6 CO2 + H2O
Balance H: C6H14O4 + O2 6 CO2 + 7H2O
At this point, the right side contains 19 O atoms whereas the left only contains 4. To
get 15 more O atoms we need to add 15/2 more O atoms by multiplying it with O2.
Balance O: C6H14O4 + (15/2) O2 6 CO2 + 7H2O
Now remove the fraction by multiplying the whole equation by 2.
2C6H14O4 + 15 O2 12 CO2 + 14 H2O
Remember to check both sides to see that both sides contain equal amounts of
each element present.
Problem: Write a balanced equation for the complete combustion of C8H18, a
gasoline component.
Solution: 2C8H18 + 25O2 16CO2 + 18H2O
States of Matter
The states of matter in a chemical equation are represented by subscript symbols
next to the compound.
(g) gas (l) liquid (s) solid
Example: 2C8H18(l) + 25O2(g) 16CO2(g) + 18H2O(l)
Another common symbol which is used for reactants or products dissolved in water
is (aq): aqueous solution.
Reaction Conditions
A simple chemical equation cannot convey the information of how to carry out the
reaction in an experiment. However there are symbols that tell us what must be
done for the reaction to occur.
Example: Δ which means to heat up as in the decomposition reaction of silver oxide:
2 Ag2O (s) Δ 4 Ag (s) + O2 (g)
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Document Summary

A chemical reaction is a process in which one set of substances (reactants) is converted to a new set of substances (products). The main evidences that prove that a chemical reaction has occurred are: colour change, formation of a solid (precipitate) within a clear solution, evolution of a gas, evolution or absorption of heat. To write the shorthand representation of a chemical equation certain steps must be followed. Consider the chemical reaction: nitrogen monoxide + oxygen nitrogen dioxide: write the reaction using chemical symbols. No + o2 no2: balance the chemical equation. Remember these rules when balancing an equation: an equation can be balanced only by adjusting the coefficients of formulas, never introduce extraneous atoms to balance. When balancing equations, using these strategies will result in efficient balancing of chemical equations. Balance elements that occur in only one compound of each side first. Balance unchanged polyatomics (or other groups of atoms) as groups.

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