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February 9th, 2017 Name: _________________________
Unit 2: Chemical ReactionsNotes: Part 5
Introduction to Chemical Reactions
TEXT p. 218-219 (word equations)
Chemistry is all around us!Remember the graphic organizer you filled out on the first day?Go back and have a look!
There are many chemical reactions – too many to count in fact!
Like many other areas in science,chemical reactions have to be grouped to stay organized.
You know how we scientist types are about organization!
To group them – we must recognize patterns.
We have already grouped other things in chemistry:- Ionic vs. molecular- Acid vs. base
Being able to recognize the patterns in chemical reactions will help us to:
Understand the reaction Predict the products of similar reactions
FIRST:
We must lay the ground workand learn the conventions
Science 1206 Unit 3: Chemical Reactions Page 1 of 38
for representing a chemical reaction simply.
Word Equations
- Used to easily represent a chemical reaction using words and symbols
Generally:
all reactants all products
OR
reactant 1 + reactant 2 product 1 + product 2
Read as:
reactant one plus reactant two goes to product one plus product two
Example:
Complete: Try This Activity: Completing Word Equations p. 219
Science 1206 Unit 2: Chemical Reactions Page 2 of 38
What do you notice?
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Homework- Questions p. 219 #’s 2, 3, 4a
Writing a Chemical Equation
If we are given a word equation
Science 1206 Unit 2: Chemical Reactions Page 3 of 38
THEN
we are able to write a chemical equation by replacing the words with chemical formulas
(this is where all your naming practice comes in handy!)
State of matter
- We must also include the state for each compound in the reaction;- It goes in brackets after each chemical formula- Most of the time this information will be given in the word problem.- We will learn later how to use a solubility table.
Solid (s) – all solids including metals and precipitates
Liquid (l) – for pure liquids such as water
Gas (g) – gaseous substances like many molecular compounds
Aqueous (aq) – compounds dissolved in water (solutions) including acids
- Activity: Worksheet – Writing Chemical Equations (pages 5, 6 and 7)
Science 1206 Unit 2: Chemical Reactions Page 4 of 38
Science 1206 Unit 2: Chemical Reactions Page 5 of 38
Writing Chemical EquationsWrite the word equations for each of the following chemical reactions:
Science 1206 Unit 2: Chemical Reactions Page 6 of 38
1) When dissolved beryllium chloride reacts with dissolved silver nitrate in water, aqueous beryllium nitrate and silver chloride powder are made.
2) When isopropanol (C3H8O) burns in oxygen, carbon dioxide, water, and heat are produced.
3) When dissolved sodium hydroxide reacts with sulfuric acid (H2SO4), aqueous sodium sulfate, water, and heat are formed.
4) When fluorine gas is put into contact with calcium metal at high temperatures, calcium fluoride powder is created in an exothermic reaction.
5) When sodium metal reacts with iron (II) chloride, iron metal and sodium chloride are formed.
The Law of Conservation of Mass
TEXT p. 222-223 (conserving mass)
Science 1206 Unit 2: Chemical Reactions Page 7 of 38
Think about some of the chemical reactions you are familiar with like:A nail becoming rusty – rust is added - nail gains massWood burning in your woodstove – all that’s left is a few ashes - mass is lost
In fact, it seems like mass is gained or lost in many reactions.
However:Through much experimentation,scientists have discovered that
mass is NOT gained or lost in any chemical reaction.Rather, it is conserved.
Every Single Time!
That is:Mass of the reactants = the mass of the
productsALWAYS
This has become known as:
The Law of Conservation of Mass- In a chemical reaction the total mass of the reactants is always equal to the total mass
of the products
Let’s revisit our woodstove example…
Science 1206 Unit 2: Chemical Reactions Page 8 of 38
And getting a little more technical…
Homework
- Questions p. 223 # 1-4 Balancing Chemical Equations
TEXT p. 226-229 (balancing chemical equations)
What does this tell us about the number and type of atoms in the reactants versus the number and type of atoms in the products?
Science 1206 Unit 2: Chemical Reactions Page 9 of 38
They MUST be the same – exactly the same…ALWAYS
During the chemical reaction the atoms become rearranged to form new products.
Because the oxygen atoms are not equal on the product side, we add another water molecule.
Now the hydrogen atoms are not equal on the reactant side, so we add another hydrogen molecule.
Look what we have:
BTW…- The numbers that we are placing in front of each compound to balance the equation are
called coefficients- They do NOT change the chemical formula
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Let’s try this:
Check your answer:
Hints for balancing:
- It doesn’t matter which side of the chemical equation you start on.- It usually helps to start with an atom that there is the most of.- Gradually work your way back and forth from reactants to products side until all atoms are
balanced.- When balancing combustion reactions (hydrocarbon and oxygen) balance in the order of C-H-O.
Examples:
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Science 1206 Unit 2: Chemical Reactions Page 12 of 38
Activity: Worksheet – Balancing Equations (Double Sided – pages 13 and 14)
Science 1206 Unit 2: Chemical Reactions Page 13 of 38
Unit 2: Chemical ReactionsNotes: Part 6
Solubility
So far we have learned many things about chemical reactions:- How to write them
Science 1206 Unit 2: Chemical Reactions Page 14 of 38
- How to balance themNext:
- We must learn how to write the states for each compound in a chemical reaction.- We have already learned the abbreviations.
o Solid (s) – all solids including metals and precipitateso Liquid (l) – for pure liquids such as watero Gas (g) – gaseous substances like many molecular compoundso Aqueous (aq) – compounds dissolved in water (solutions) including acids
- Before, the solubility information would be given BUT in this section we will learn how to use the solubility table on the back of the periodic table to predict the solubility of
ionic compounds.Solubility Table
- Contains general solubility guidelines for ionic compounds
Can be used in just 2 easy steps!
Step 1: Look for the anion (negative ion) of the compound in the top of the columns.
Step 2: Look down the column to locate the cation (positive ion) and determine if it is in the…
- high solubility row - write (aq) after the compound in the chemical equation- low solubility row - write (s) after the compound in the chemical equation.
o HINT: this is generally the precipitate in the products!
Science 1206 Unit 2: Chemical Reactions Page 15 of 38
TRY: Potassium chloride
Silver sulfate
Ammonium fluoride
Copper (II) acetate
Copper (I) acetate
Activity 2.18: Worksheet – Predicting Solubility (page 17)
Science 1206Unit 2: Chemical Reactions
Predicting Solubility - Worksheet
Place the subscript (s, l, g, aq) indicating the correct state of matter in the brackets at the end of each element/compound.
1. __ Cr2O3( ) __ Cr( ) + __ O2( )
Science 1206 Unit 2: Chemical Reactions Page 16 of 38
2. __ Ni( ) + __ HCl( ) __ NiCl2 ( ) + __ H2( )
3. __ Ca(NO3)2( ) + __ Na3PO4 ( ) __ Ca3(PO4)2( ) + __ NaNO3( )
4. __ Al ( ) + __ O2 ( ) __ Al2O3 ( )
5. __ HCl ( ) + __ Ca(OH)2 ( ) __ HOH ( ) +__ CaCl2 ( )
6. __Zn ( ) + __ Pb(CH3COO)2 ( ) __ Pb( ) + __ Zn(CH3COO)2( )
7. __ HgO ( ) __ Hg ( ) +__ O2 ( )
8. __ NaI ( )+__ Pb(NO3)2 ( ) __ PbI2 ( )+ __ NaNO3 ( )
9. __ Cl2 ( ) +__ NaI ( ) __ I2 ( ) + __ NaCl ( )
10. __ Al2(SO4)3 ( ) + __ Ca(OH)2 ( ) __ Al(OH)3 ( )+ __ CaSO4 ( )
Types of Chemical Reactions
TEXT p. 230 (combustion)p. 233-235 (synthesis and decomposition)p. 240-241 (single/double replacement)
So far we have learned many things about chemical reactions:- How to write them- How to balance them- How to predict solubility
Next:
Science 1206 Unit 2: Chemical Reactions Page 17 of 38
We must learn:- How to identify different types- How to predict products
All members of a chemical family react in a similar way
There are definite patterns in reactions
Knowledge of patterns is useful because:
o We will have a better understanding of chemical reactionso We can predict products of unknown reactions
Remember! You need to be able to PREDICT the products!
There are 5 types of chemical reactions that we will be studying.
1. Hydrocarbon Combustion- rapid reaction of a substance with oxygen to produce oxides- Often called burning- General Format: Hydrocarbon + oxygen carbon dioxide + water
Example:
Butane + oxygen carbon dioxide + water vapor
2C4H10 + 13 O2 8CO2 + 10 H2O
Balancing tip: Remember to balance in the order of C-H-O
Try these! Include:
Science 1206 Unit 2: Chemical Reactions Page 18 of 38
- Word equation (if not already given)- Balanced chemical equation- States of matter
#1: Methane + oxygen carbon dioxide + water vapor
#2: Kerosene C14H30 (l) under goes complete combustion.
Activity: Worksheet – Combustion Reactions (page 20)
Science 1206 Unit 2: Chemical Reactions Page 19 of 38
2. Synthesis- also called combination or formation reactions- combination of smaller atoms or compounds to form 1 larger compound (product)- General Format: A + B AB- Often elements combine to form compounds
Science 1206 Unit 2: Chemical Reactions Page 20 of 38
Examples:Hydrogen + oxygen water
2H2 + O2 2H2O
Hydrogen chloride + ammonia ammonium chloride
HCl + NH3 NH4Cl
Try this! Include:
- Word equation (if not already given)- Balanced chemical equation- States of matter
#1: Potassium reacts with fluorine.
Science 1206 Unit 2: Chemical Reactions Page 21 of 38
3. Decomposition- The splitting of one compound (reactant) into elements or smaller compounds- General format: AB A + B
Examples:2H2O2 2H2O + O2
Decomposition of hydrogen peroxide H2O2
Decomposition of water (hydrolysis)
Try this! Include:
- Word equation (if not already given)
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- Balanced chemical equation- States of matter
#1: Mercury (II) oxide is heated.
Activity: Worksheet – Formation and Decomposition Reactions (pages 24-25)
Science 1206 Unit 2: Chemical Reactions Page 23 of 38
Science 1206 Unit 2: Chemical Reactions Page 24 of 38
4. Single Replacement- Also called single displacement- Involves one element and one compound as reactants- One element replaces (displaces) the other “like” element in the compound
o Metal element replaces the metal element in the compoundo Non-metal element replaces the non-metal element in the compound
- General format:
o Z + AB A + ZB (where Z and A are metals)
o Y + AB B + AY (where Y and B are non-metals)
Examples:2FeI2+Pb→PbI4+2Fe (metal replaces metal)
FeI2+Cl2→FeCl2+I2(non-metal replaces non-metal)
Science 1206 Unit 2: Chemical Reactions Page 25 of 38
Try this! Include:
- Word equation (if not already given)- Balanced chemical equation- States of matter
#1: Aluminum is added to a solution of sulfuric acid.
Activity: Worksheet – Single Replacement Reactions (page 28 and 29)
Science 1206 Unit 2: Chemical Reactions Page 26 of 38
Science 1206 Unit 2: Chemical Reactions Page 27 of 38
Science 1206 Unit 2: Chemical Reactions Page 28 of 38
5. Double replacement- Also called double displacement- Like elements in different compounds replace (displace) each other
- General format: AB + XY AY + XBo Where A and X are metalso Where B and Y are non-metals
Examples:
HCl(aq)+ NaOH(aq)→NaCl(s)+H2O(l)
CaCO3(aq)+2HCl(aq)→CaCl2(s)+H2CO3(aq)
NOTE:
Science 1206 Unit 2: Chemical Reactions Page 29 of 38
Neutralization reactions between acids and bases are double replacement reactions.
Johnny, finding life a bore,Drank some H2SO4.
Johnny's father, an MDGave him CaCO3.
Now he's neutralized it's true,But he's full of CO2.
Try this! Include:
- Word equation (if not already given)- Balanced chemical equation- States of matter
#1: A solution of potassium phosphate reacts with cobalt (III) chloride
Activity: Worksheet –Double Replacement Reactions (page 32 and 33)
Science 1206 Unit 2: Chemical Reactions Page 30 of 38
Science 1206 Unit 2: Chemical Reactions Page 31 of 38
To Summarize:Science 1206 Unit 2: Chemical Reactions Page 32 of 38
AND:
Combustion
Activity: Worksheet –Predicting Chemical Reaction Type (page 35)
Science 1206 Unit 2: Chemical Reactions Page 33 of 38
Science 1206Predicting Chemical Reaction Type
Instructions:
Classify each reaction as simple composition (sc), simple decomposition (sd), complete combustion (c), single replacement (sr), double replacement (dr) or other (o).
Classification1. Al(NO3)3(aq) + Na2CO3(aq) Al2(CO3)3(s) + NaNO3(aq) .
2. CaCO3(s) Ca(s) + C(s) + O2(g)
3. CH3OH(l) + O2(g) CO2(g) + H2O(g) .
4. BaO(s) + HOH(l) Ba(OH)2(s) .
5. F2(g) + MgCl2(aq) MgF2(aq) + Cl2(l) ,
6. H2O2(l) H2O + O2(g) .
7. C3H5(OH)3 + O2(g) CO2(g) + H2O(g) .
8. Ba(OH)2(aq) + HNO3(aq) HOH(l) + Ba(NO3)2(aq) .
9. C3H6 (g) + O2(g) CO2(g) + H2O(g) .
10. AgCl(s) Ag(s) + Cl2(g) .
11. Mg(s) + O2(g) MgO(s) .
12. Mg(s) + HCl(aq) MgCl2(aq) + H2(g) .
13. SrO(s) + CO2(g) SrCO3(s) .
14. Li(s) + O2(g) Li2O(s) .
15. Fe2O3(s) + HCl(aq) FeCl3(aq) + H2O(l) .
Unit 2: Chemical ReactionsScience 1206 Unit 2: Chemical Reactions Page 34 of 38
Notes: Part 6
Core Lab #6: Single Displacement and Double Displacement Reactions
TEXT: p. 242-245
Complete the worksheet and submit for grading.
YEAH! – No write-up!
Science 1206 Unit 2: Chemical Reactions Page 35 of 38
Chemical Reactions and Energy
TEXT: p. 281 (exothermic and endothermic reactions)
Some chemical reactions seem to speed up as they progress
- A forest fire burns slowly at first and then may burn out of control.
What Happens:
- Temperature speeds up reactions rates because it increases the motion of particles which in turn increases the collisions between particles that result in a chemical change.
- That means that the heat energy released by the forest fire actually works to increase the rate of combustion.
Other reactions release energy (heat):
- Water freezing- Rubbing alcohol evaporating- Dynamite exploding
Chemical changes that release energy:
Exothermic
Chemical changes that require an input of energy:
Endothermic
Exothermic Reactions
Example: gasoline + oxygen carbon dioxide + water + heat energy
Some physical changes can be exothermic
Example: sulfuric acid (l) sulfuric acid (aq) + heat
(psst – always add acid to water)
An energy diagram can be used to graph the energy changes in an exothermic reaction.A + B -> C + D + Heat
Science 1206 Unit 2: Chemical Reactions Page 36 of 38
Endothermic Reactions
Some reactions require heat energy on a continuous basis for the change to take place
- Heat can be absorbed from the surroundings- These changes do not speed up because surrounding temperature drops as heat is
absorbed.
Example: water (s) + heat energy water (l)
Energy diagram for an endothermic reaction
Heat + A + B -> C + D
Science 1206 Unit 2: Chemical Reactions Page 37 of 38
Review
Chapter 5: p. 214-215 # 1 a) to d), 2 b) to f), 3 b) to h), 4, 5, 6, 7, 8, 9, 10, 11, 15
Chapter 6: # 1-10
Chapter 7: # 11
Chapter 8: 5, 6, 9, 16, 19
Unit 3 is CompleteFan-tab-u-lous!
Science 1206 Unit 2: Chemical Reactions Page 38 of 38
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