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Balancing reactions and different types of reactions
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Chemical Reactions
Chapter 11
Using Everyday Equations
Every minute of the day chemical reactions are taking place both in and around you.
What makes something a chemical reaction?
A chemical reaction involves one or more substances, the reactants, changing into one or more substances, the products.
Reactants Products
“ ” means “yields” or “reacts to produce.”
3
Chemical reactions can be described many ways. One is by using a word equation.
A word equation is an equation where reactants and products are represented by words.
Example:
methane + oxygen carbon dioxide + water
Word equations, while useful, are cumbersome. To better describe a reaction, writing the formulas is used.
A chemical equation uses formulas of reactants (on the left) separated by an arrow from products (on the right).
Example:
Fe + O2 Fe2O3
(Skeleton equation)
- does not indicate the relative amounts of reactants and products
Most often symbols are used to describe the state (i.e., gas, solid, etc.) of each substance
Balancing Chemical Reactions
• Coefficients are small whole numbers that are placed in front of the formulas in an equation in order to balance it.
• A chemical reaction is also described by a balanced equation in which each side of the equation has the same number of each element and mass is conserved.
How do you write a balanced chemical equation?
• To write a balanced chemical equation-
1. First write the skeleton equation.
2. Then use coefficients to balance the equation so that it obeys the law of conservation of mass.
• What is the Law of Conservation of Mass?
Practice
__ H2 + ___ O2 ___ H2O
__ SO2 + ___ O2 ___ SO3
Try to balance this reaction:__Al(OH)3(s) + __H2SO4(aq) __Al2(SO4)3(aq) + __H2O(l)
Al
S
H
O
Al
S
H
O
1
1
5
7
2
3
2
13
12
18
8
2 3 6
2
10
3
12
18
Balance these equations
• __ Mg + __ O2 → __ MgO
• __ KClO3 → __ KCl + __ O2
• __ Cu + __ AgNO3→ __ Cu(NO3)2 + __ Ag
• __KOH + __ H3PO4 → __ K3PO4 + __ H2O
• 2 Mg + O2 → 2 MgO
• 2 KClO3 → 2 KCl + 3 O2
• Cu + 2 AgNO3→ Cu(NO3)2 + 2 Ag
• 3 KOH + H3PO4 → K3PO4 + 3 H2O•Even better…•2 Mg (s) + O2 (g) → 2 MgO (s)
Types of Reactions
• There are five types of chemical reactions we will talk about:
1. Synthesis reactions
2. _____________ reactions
3. Single displacement reactions
4. ________________ reactions
5. Combustion reactions
• You need to be able to identify the type of reaction and predict the product(s)
Steps to Writing Reactions• Some steps for doing reactions
1. Identify the type of reaction
2. Predict the product(s) using the type of reaction as a model
3. Balance it
Don’t forget about the diatomic elements! (BrINClHOF) For example, Oxygen is O2 as an
element.
In a compound, it can’t be a diatomic element because it’s not an element anymore, it’s a compound!
1. Synthesis reactions• Synthesis reactions occur when two
substances (generally elements) combine and form a compound. (Sometimes these are called combination or addition reactions.)
reactant + reactant 1 product• Basically: A + B AB
• Example: 2H2 + O2 2H2O
• Example: C + O2 CO2
Practice
• Predict the products. Write and balance the following synthesis reaction equations.
• Sodium metal reacts with chlorine gas
Na(s) + Cl2(g)
• Solid Magnesium reacts with fluorine gas
Mg(s) + F2(g)
• Aluminum metal reacts with fluorine gas
Al(s) + F2(g)
2. Decomposition Reactions• Decomposition reactions occur when a
compound breaks up into the elements or in a few to simpler compounds
• 1 Reactant Product + Product
• In general: AB A + B
• Example: 2 H2O 2H2 + O2
• Example: 2 HgO 2Hg + O2
Practice
• Predict the products. Then, write and balance the following decomposition reaction equations:
• Solid Lead (IV) oxide decomposes PbO2(s)
• Aluminum nitride decomposes
AlN(s)
Practice
Identify the type of reaction for each of the following synthesis or decomposition reactions, and write the balanced equation:
N2(g) + O2(g)
BaCO3(s)
Co(s)+ S(s)
NH3(g) + H2CO3(aq)
NI3(s)
(make Co be +3)
Nitrogen monoxide
3. Single Replacement Reactions
• Single Replacement Reactions occur when one element replaces another in a compound.
• A metal can replace a metal (+) OR a nonmetal can replace a nonmetal (-).
• element + compound product + product A + BC AC + B (if A is a metal) ORA + BC BA + C (if A is a nonmetal)
(remember the cation always goes first!)
When H2O splits into ions, it splits intoH+ and OH- (not H+ and O-2 !!)
We have looked at several reactions:Fe + CuSO4 Cu + Fe2(SO4)3
Li + H2O LiOH + H2
Such experiments reveal trends. The activity series ranks the relative reactivity of metals.It allows us to predict if certain chemicals will undergo single displacement reactions when mixed: metals near the top are most reactive and will displacing metals near the bottom.Q: Which of these will react?
Fe + CuSO4 Ni + NaCl Li + ZnCO3 Al + CuCl2
Cu + Fe2(SO4)3
Yes, Fe is above Cu
NR (no reaction)
No, Ni is below Na
Zn + Li2CO3Cu + AlCl3
Yes, Al is above Cu
KNaLiCaMgAlZnFeNiSnPbH
CuHgAgAu
Yes, Li is above Zn
H is the only nonmetal listed. H2 may be displaced from acids or can be given off when a metal reacts with H2O (producing H2 + metal hydroxide). The reaction with H2O depends on metal reactivity & water temp. Q: will Mg react with H2O?
KNaLiCaMgAlZnFeNiSnPbH
CuHgAgAu
cold H2O
hot H2O
steam
acid
NR
A: No for cold, yes if it is hot/steamMg + H2O
H2 + ZnCl2Complete these reactions:Al + H2O(steam) Cu + H2O Ca + H2SO4 Na + H2O
H2 + Mg(OH)2
H2 + Al(OH)3
H2 + CaSO4
H2 + NaOH
Q: Zn + HCl
• All metals will have a specific place in the activity series. For simplicity, only the most common metals are shown.
• The metals near the top of the activity series are more reactive because their valence electrons are more easily removed.
• On tests and exams the activity series may appear as K, Na, … Ag, Au; you must remember that K is reactive, Au is not.
• If the valence of a metal is not indicated in the question, use its most common valence (in bold on your periodic table) to determine the correct chemical formula.
Other Activity Series Information
Single Replacement Reactions
• Write and balance the following single replacement reaction equation:
• Zinc metal reacts with aqueous hydrochloric acid
Zn(s) + HCl(aq) ZnCl2 + H2(g)
Note: Zinc replaces the hydrogen ion in the reaction
2
Single Replacement Reactions• Sodium chloride solid reacts with fluorine gas
NaCl(s) + F2(g) NaF(s) + Cl2(g)
Note that fluorine replaces chlorine in the compound
• Aluminum metal reacts with aqueous copper (II) nitrate
Al(s)+ Cu(NO3)2(aq)
2 2
4. Double Replacement Reactions
• Double Replacement Reactions occur when a metal replaces a metal in a compound and a nonmetal replaces a nonmetal in a compound
• Compound + compound product + product
• AB + CD AD + CB
Double Replacement Reactions
• Think about it like “foil”ing in algebra, first and last ions go together + inside ions go together
• Example:
AgNO3(aq) + NaCl(s) AgCl(s) + NaNO3(aq)
• Another example:
K2SO4(aq) + Ba(NO3)2(aq) KNO3(aq) + BaSO4(s) 2
Practice
• Predict the products. Balance the equation1. HCl(aq) + AgNO3(aq)
2. CaCl2(aq) + Na3PO4(aq)
3. Pb(NO3)2(aq) + BaCl2(aq)
4. FeCl3(aq) + NaOH(aq)
5. H2SO4(aq) + NaOH(aq)
6. KOH(aq) + CuSO4(aq)
5. Combustion Reactions
• Combustion reactions occur when a hydrocarbon reacts with oxygen gas.
• This is also called burning!!! In order to burn something you need the 3 things in the “fire triangle”:1) A Fuel (hydrocarbon)2) Oxygen to burn it with3) Something to ignite the reaction (spark)
Combustion Reactions• In general:
CxHy + O2 CO2 + H2O
• Products in combustion are ALWAYS carbon dioxide and water. (although incomplete burning does cause some by-products like carbon monoxide)
• Combustion is used to heat homes and run automobiles (octane, as in gasoline, is C8H18)
Combustion
• Example• C5H12 + O2 CO2 + H2O
• Write the products and balance the following combustion reaction:• C10H22 + O2
5 68
Mixed Practice
• State the type, predict the products, and balance the following reactions:
1. BaCl2 + H2SO4
2. C6H12 + O2
3. Zn + CuSO4
4. Cs + Br2
5. FeCO3
