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Chemical ReactionsChemical Reactions
Unit 8Unit 8
Chemical Reaction vs. Chemical Chemical Reaction vs. Chemical EquationEquation
A REACTION is the process where 2 or more atoms A REACTION is the process where 2 or more atoms or compounds rearrange themselves to form new or compounds rearrange themselves to form new substancessubstances..
+
An EQUATION is written to summarize what has happened in a reaction
2H2 + O2 2H2O
Signs of a Chemical Signs of a Chemical ReactionReaction
1.1. Precipitate formedPrecipitate formed
2.2. Permanent color Permanent color changechange
3.3. Temperature Temperature changechange
4.4. Gas producedGas produced
5.5. Light producedLight produced
Law of Conservation of MassLaw of Conservation of Mass
Mass is neither created nor Mass is neither created nor destroyed in a chemical reaction.destroyed in a chemical reaction.
Mass of the products equals the Mass of the products equals the mass of the reactants in a chemical mass of the reactants in a chemical reactionreaction
Atoms only rearrange themselvesAtoms only rearrange themselves
Practice ProblemsPractice Problems
Example 1: What is the total mass of reactants in the reaction below?2 H2 + O2 2 H2O Answer: __________g ? 72 g
Example 2: What is the total mass of products in the reaction below?
AgNO3 + NaCl AgCl + NaNO3 Answer: __________g 170 g 56 g ---------?----------
Example 3: What is the mass of zinc produced in the reaction below?
Ca + ZnCO3 CaCO3 + Zn Answer: __________g
40 g 125 g 100 g ?
72
226
65
Chemical EquationsChemical Equations
Reactants (2HReactants (2H22(g) and O(g) and O22(g))(g))
Products (2HProducts (2H220 (g))0 (g))
2H2H22((gg) + O) + O22((gg) ) 2H 2H22O(O(gg))
– Coefficient (The large number in front of HCoefficient (The large number in front of H22 and H and H220)0)
– Chemical formulaChemical formula
– Physical statePhysical state (s- solid; g- gas; aq- aqueous; l- liquid)(s- solid; g- gas; aq- aqueous; l- liquid)
Diatomic ElementsDiatomic Elements
These elements are never found by These elements are never found by themselves in nature. themselves in nature.
II22, Br, Br22, Cl, Cl22, F, F22, O, O22, N, N22, H, H22
To help you remember, memorize To help you remember, memorize this:this:
II BrBring ing ClClay ay FFor or OOur ur NNew ew HHutut
Some other stuff you may Some other stuff you may see:see:
Δ Δ heat added to reactants (triangleheat added to reactants (triangle
appears above arrow)appears above arrow) CatalystsCatalysts are substances that are substances that
increase the rate of the reaction but increase the rate of the reaction but are not used up themselves. are not used up themselves. The formula The formula for the catalyst is written above the arrow: (example MnOfor the catalyst is written above the arrow: (example MnO22))
MnO22 KClO3(s)2 KClO3(s) 2KCl(s) + 3 O2(g)
Catalysts are not used up in the reaction so they appear above the arrow
Balancing EquationsBalancing Equations
Copy down equation (leave space for Copy down equation (leave space for #’s)#’s)
Make an atom inventoryMake an atom inventory– List elements on both sides List elements on both sides
(reactants/products)(reactants/products)
– Count # of atoms on each sideCount # of atoms on each side Coefficient Coefficient subscript = # of atoms subscript = # of atoms
– Reduce if necessary!Reduce if necessary!– Double Double check your work!check your work!
Types of Chemical Types of Chemical ReactionsReactions
DisclaimerDisclaimer
The events depicted in this story are fictitious. Any similarity to any person living or dead is merely coincidental.
The Story
Begins…
2H2 + O2 → 2 H2O
3Mg + N2 → Mg3N2
Synthesis Reaction
A reaction in which two or more elements form a compound.
Synthesis ReactionSynthesis Reaction
+
AB A B
The Story Continues…
Decomposition Reaction
2H2O → 2H2 + O2
2HgO → 2Hg + O2
A reaction in which a compound is broken down into two or more elements.
Decomposition ReactionDecomposition Reaction
+
AB B A
The Story Continues…
Single Replacement Reaction
2KCl + F2 → 2KF + Cl2
Mg + 2HCl → H2 + MgCl2
A reaction in which one element reacts with one compound to form another element and another compound.
Single Replacement Single Replacement ReactionReaction
+ +
AB C CB A
The Story Continues…
Double Replacement Reaction
Pb(NO3)2 + K2CrO4 PbCrO4+ 2 K(NO3)
NaCl + AgNO3 AgCl + Na(NO3)
A reaction in which the metals present in two compounds change places to form two new compounds.
The End!But…
CombustionCombustion
When a carbon compound reacts When a carbon compound reacts with oxygen to make carbon dioxide with oxygen to make carbon dioxide and water.and water.– Hint:Hint:
It will It will alwaysalways have O have O22 on reactant side on reactant side
It will It will alwaysalways have CO have CO22 and H and H22O on product O on product sideside
Example:Example:CHCH44 + O + O22 → CO→ CO22 + H + H22OO
ExamplesExamples 2NaCl 2NaCl 2Na + Cl 2Na + Cl22
CC88HH1818 + O + O22 H H22O + COO + CO22
2HCl + F2HCl + F22 2HF + Cl 2HF + Cl22
HCl + NaOH HCl + NaOH HOH + NaCl HOH + NaCl
2Na + Cl2Na + Cl22 2NaCl 2NaCl
Decomposition
Combustion
Single Replacement
Double Replacement
Synthesis