Transcript Chemical Reactions
Chemical Reactions
Chapter 10
Reactions and Equations Section 1
The process by which the atoms of one or more substances are rearranged to form different substances is called a
chemical reaction
(aka chemical change) Chemical Reaction Indicators Temperature Change (Release/absorption of energy) Color change Odor Gas formation Formation of a solid
Representing Chemical Reactions
Reactants- starting substances Products- substances that are formed during the reaction
“react to produce” or “yield”
Reactant 1 + Reactant 2 Product 1 + Product 2
Always written to the arrow’s left Always written to the arrow’s right
Symbols used in Equations
Symbol +
(s) (l) (g) (aq)
Meaning Separates two or more reactants or products Separates reactants from products Identifies solid state Identifies liquid state Identifies gaseous state Identifies water solution
Writing Equations
“ Iron and chlorine react to produce iron (III) chloride” Iron (s) + chlorine (g) Fe (s) + Cl 2 (g) iron (III) chloride (s) FeCl 3 (s)
Chemical Equation-
chemical formulas involved in a chemical reaction statement that uses Shows the number of atoms of each reactant and each product is equal on both sides of the arrow (balanced)
Practice Problems
Write skeleton equations for the following word equations hydrogen (g) + bromine (g) hydrogen bromide (g) carbon monoxide (g) + oxygen (g) carbon dioxide (g) potassium chlorate (s) potassium chloride (s) + oxygen (g)
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Steps for balancing equations
1.
2.
3.
Write the skeleton equation for the reaction.
Make sure that the chemical formulas are correctly written. Show the physical states of all reactants and products.
Count the atoms of the elements in the reactants.
If a reaction involves identical polyatomic ions in the reactants and products, count the ions as they are elements.
Count the atoms of the elements in the products.
4.
Change the coefficients to make the number of atoms equal on both sides of the equations.
NEVER change the subscript in a chemical formula to balance an equation because doing so changes the identity of the substance.
5.
Write the coefficients in their lowest possible ratio. (whole numbers)
6. CHECK YOUR WORK!
Practice Problem
Sodium hydroxide and calcium bromide react to produce solid calcium hydroxide and sodium bromide. (The reaction occurs in water)
Organizing Technique
Starting Add Coefficients Balanced
Practice Problems
Solid zinc and aqueous hydrogen sulfate react to produce hydrogen gas and aqueous zinc sulfate
Classifying Chemical Reactions Section 2
Synthesis-whenever two or more substances combine to form a single product Example: 4Fe (s) + 3 O 2(g) 2Fe 2 O 3 (s) General Equation:
element/compound + element/compound
compound A + B
AB
Combustion- a substance reacts with oxygen to produce carbon dioxide and water Example: CH 4(g) + 2O 2(g) CO 2(g) + 2 H 2 O (g) General Equation:
Organic Compound + Oxygen
Organic Compound + O 2(g) H 2 O (g) Carbon Dioxide + Water
CO 2 (g) +
Combustion reactions and light oxygen combines with a substance and releases energy in the form of heat
Decomposition-a compound breaks down into two or more elements or new compounds Example: NH 4 NO 3(s) N 2 O (g) + 2H 2 O (g) General Equation: compound two or more elements/compound
AB
A + B Practice Problems: 1.
The solids aluminum and sulfur react to produce aluminum sulfide.
2.
Ethane gas (C 2 H 6 ) burns in air, producing carbon dioxide gas and water vapor 3.
Nickel (II) hydroxide (s) decomposes to produce nickel (II) oxide (s) and water.
Replacement Reactions
Single Replacement-one element takes the place of another element in a compound Example: Fe (s) + CuSO 4(aq) General Equation: element A + compound BX
A + BX
FeSO 4(aq) + Cu (s) compound AX + element B
AX + B
HAVE TO USE THE ACTIVITY SERIES THE METAL WILL BE REPLACED. TO SEE IF IF METAL (A) IS LOCATED ABOVE METAL (B), IT WILL REPLACE IT. (IF NOT, WRITE NO REACTION (NR)
Practice Problems K
(s)
+ ZnCl
2 (aq)
Cl
2 (g)
+ HF
(aq)
Fe
(s)
+ CuSO
4 (aq)
Double-Replacement Reactions
Double Replacement- the positive portions for two ionic compounds are interchanged Example: Pb(NO 2KNO 3 (aq) 3 ) 2 (aq) + 2KI (aq) PbI 2 (s) + General Equation: compound AB + compound CD compound AD + compound CB
AB + CD
AD + CB
NOTE: A PRECIPITATE OR WATER MUST BE FORMED!!
TO PREDICT THIS, USE THE SOLUILITY RULES TO SEE IF A PRECIPITATE IS FORMED, FOLLOW THE DIRECTIONS TO THE CHART FOR THE COMPOUNDS OF THE PRODUCTS FORMED
Practice Problems
1.
2.
Aqueous lithium iodide and aqueous silver nitrate react to produce solid silver iodide and aqueous lithium nitrate. BaCl 2(aq) + K 2 CO 3 (aq)
Section Assessment
What are the five classes of chemical reactions?
Identify two characteristics of combustion reactions.
Compare and contrast single replacement reactions and double replacement reactions.
Reactions in Aqueous Solutions Section 3
Review: solution = homogeneous mixture
Solutes
- the particles dissolved in the solution
Solvent
- water (in most cases)- what does the dissolving Aqueous solution- a solution in which water is the solvent
When two aqueous solutions that contain ions as solutes are combined, the ions may react with one another. (double-replacement reaction occurs) Three types of products form from the DR-reaction Precipitate (type of solid) Water Gas
Ionic Equations
Complete Ionic Equation the particles in a solution as they realistically exist show all of Spectator Ions Ions that do not participate in a reaction Net Ionic Equation-
and/or gas)
include only the particles that participate in the reaction (forming a precipitate, water
Example
Pb(NO 3 ) 2 (aq) + 2KI (aq) → 2KNO 3 (aq) + PbI 2 (s)
Pb(NO 3 ) 2 (aq) + 2KI (aq) → 2KNO 3 (aq) + PbI 2 (s) 1.
Complete Ionic Equation: Pb +2 (aq) + 2NO 3 -1 (aq) + 2K + (aq) + 2I (aq) 2K + (aq) + 2NO 3(aq) + PbI 2(s) 2.
Cross out spectator ions Pb +2 (aq) + 2NO 3 -1 (aq) + 2K + (aq) + 2I (aq) 2K + (aq) + 2NO 3(aq) + PbI 2(s) 3.
Net Ionic Equation Pb +2 (aq) + 2I (aq) PbI 2(s)
Your turn!
Aqueous solutions of lithium sulfate and calcium nitrate are mixed, forming the precipitate calcium sulfate Steps to remember: 1.
Write out complete balanced 2.
3.
4.
Complete ionic equation Get rid of spectator ions Net ionic equation (DR) reaction (with states)