Chemical Reactions Chapter 10
Dec 30, 2015
Representing Chemical Changes Chemical equations are used to
represent chemical reactions (the process by which one or more substances are changed into one or more different substances).
Evidence of chemical reactions Pg. 277 list types of evidence that
a chemical reaction has occurred Temperature change Energy released in form of heat
and light Color change Odor Gas bubbles Appearance of a solid ( precipitate)
A correct chemical equation shows:
what changes take place the relative amounts of the
elements compounds that take part in the
changes
Representing Chemical Changes
Reactants are the starting substances in a chemical reaction.
Products are the substances formed by the chemical reaction.
Representing Chemical ChangesReactants yield Products
C2H2(g) + O2(g)
reactants
CO2 (g) + H2O(l)
productsyield
C2H2(g) + O2(g) CO2 (g) + H2O(l) The letters in parenthesis represent the physical
states. g = gases l = liquids s= crystalline solid (also represented “cr”). aq = substance dissolved in water
Representing reactions
Word equations Skeleton equations
-Formulas and states are represented, but not amounts – equation not balanced
Left pg. entry practice problems1. Hydrogen bromide gas is
produced from the reaction between hydrogen gas and bromine gas
2. Write a skeleton equation. Pg. 279 practice problems
Balancing Equations Reactants are written on the left
side of the chemical equations. Products are written on the right.
Balancing Equations Use the following steps to balance
equations:1. Determine the reactants and the products.
2. Assemble the parts of the chemical equation. The symbols and the formulas must be correct.
3. Balance the equation. Balanced equations have the same kind and number of atoms on each side. In a chemical reaction no mass is lost or gained. Law of conservation of mass
Balancing Equations
Balance the equation(continued) The same amount of matter is present before and after the reactions. Coefficients, not subscripts, may be changed to balance an equation. Never change a subscript to balance an equation.
Balancing Equations
Balance the equation(continued) The same amount of matter is present before and after the reactions. Coefficients, not subscripts, may be changed to
balance an equation. Never change a subscript to balance an equation.
EVER! Don’t do it !!!
Balancing Equations
Notice one C in carbon dioxide and six carbons in glucose.
CO2 + H2O C6H12O6 + O2
C6H12O6CO2
Balancing Equations
Multiply the carbon dioxide by six to equal the six carbons in glucose.
CO2 + H2O C6H12O6 + O2
C6H12O6CO2
6
Balancing Equations
Next look at the water molecule.
Notice that there are 12 H in glucose. Therefore you’ll need six waters to balance.
CO2 + H2O C6H12O6 + O26 6
Balancing Equations
Next, count the total oxygen atoms on the reactant side and compare that to the product side.
CO2 + H2O C6H12O6 + O26 6
(6x2) + (6x1)
=18
6
18 - 6= 12 2 =
Balancing Equations
Finally, Check all atoms, comparing both sides.
6CO2 + 6H2O C6H12O6 + 6O2
6 C = 6 C 12 H = 12 H 18 O = 18 O
End of Part IPractice problems
pg.282 #’s 4-6
4. In water, iron(III) chloride reacts with sodium hydroxide, producing solid iron(III) hydroxide and sodium chloride.
Types of Chemical Reactions
Single Replacement (Displacement) Double Replacement (Displacement) Decomposition Synthesis Combustion
Anions swap places
Double Displacement
compound AB + compound CD compound AD + compound CB
PbCl2 + Li2SO4
Re
PbSO4 + 2LiCl