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Writing Chemical Equations
§ Chemical reactions occur every day.
Digesting photosynthesis cooking § In a chemical reaction, one or more reactants are converted to one or more new products.
Evidence of chemical reactions How do you know if a chemical reaction has occurred? § Change in energy (gets hot or cold)
§ Produce a gas (bubbles) § Color change § Form a precipitate= form solid from 2 liquids
Symbols to know Yield (produces) Reaction in both directions
(s) Solid
(l) Liquid
(aq) Aqueous= Dissolved in water
(g) gas
H2SO4 (aq)à H2 (g) + S (s) + 2O2 (g) Subscript # = number of atoms of each element Coefficients—before the symbol, used to balance equations
Represent Reactions with chemical equations § Word equations
Ex: Iron reacts with oxygen gas to produce iron (III) oxide. ú Iron + oxygen gas à iron (III) oxide How many reactants and products in the following? 1. Hydrogen peroxide decomposes to produce water and oxygen gas Hydrogen peroxide à water + oxygen 2. Methane and oxygen gas react to produce carbon dioxide and water
Methane + oxygen à carbon dioxide + water
Chemical Equation § Chemical equations replace words with formulas. § Skeleton chemical equations do NOT show the relative abundance of each chemical. ú THEY ARE UNBALANCED.
Ex: Oxygen and hydrogen combine to form water
O2 (g) + H2(g)à H2O(l)
Balancing Chemical Equations Subscripts—used in formulas Coefficients—before the symbol, used to balance equations
§ Solid sulfur burns in the presence of oxygen to form sulfur dioxide gas.
§ Iron reacts with oxygen gas to produce iron (III) oxide.
ú YOU CANNOT CHANGE SUBSCRIPTS TO BALANCE!!!
S(s) + O2 (g) à SO2(g)
Fe(s) + O2(g) → Fe2O3(s) 4Fe(s) + 3O2(g) → 2Fe2O3(s)
H2 (g) + O2 (g) à H2O (l)
Write the chemical equations, then balance 1. Solid Iron reacts with oxygen gas to produce
iron (III) oxide (rust).
2. Aqueous Hydrogen peroxide (H2O2) decomposes to produce water and oxygen gas.
3. Solid sulfur burns in the presence of oxygen gas to form sulfur dioxide gas.
Fe(s) + O2(g) → Fe2O3(s)
H2O2(aq) → H2O (l)+ O2(g)
S(s) + O2(g) → SO2(g)
2Fe(s) + 3O2(g) → 2Fe2O3(s)
2H2O2(aq) → 2H2O (l)+ O2(g)
S(s) + O2(g) → SO2(g)
Write the Coefficient to Balance -‐ balance the more complicated molecule first, then single molecules
1. ___H2 (g) + ___O2 (g) à ___H2O (l)
2. ___Ag2S (s) + ___Al(s) à ___Ag(s) + ___Al2S3 (s)
3. ____AgNO3 + ____H2S à ___Ag2S + ____HNO3
4. When heated, solid potassium chlorate decomposes to form solid potassium chloride and oxygen gas. 2KClO3(s) → 2KCl(s) + 3O2(g)
2 2
Warm up 1. What is a chemical reaction? 2. What is conservation of mass? 3. How are the two concepts above
related? 4. When heated, solid potassium chlorate
decomposes to form solid potassium chloride and oxygen gas. Write the balanced equation. (chlorate = ClO3
-‐1) 2KClO3(s) → 2KCl(s) + 3O2(g)
Why Balance?? § Law of conservation of mass says so…
Law of Conservation of Mass: -‐ Total mass of the universe is constant -‐ Mass can not be created or destroyed -‐ In a closed system, mass can not change quantity (though it can change form)
Balancing Equations -‐
1. __Li(s) + __Cl2(g) → __LiCl(s) 2. __Fe(s) + __O2(g) → __Fe2O3(s) 3. __H2O2 → __H2O + O2 4. __KClO3(s) → __KCl(s) + __O2(g) 5. __P4(s) + __Cl2(g) → __PCl3(l)
Write the balanced equation by filling in the coefficients. If the coefficient is 1, you don’t write anything
6. Aluminum metal reacts with oxygen gas to produce aluminum oxide solid.
7. Gaseous nitrogen dioxide decomposes to form dinitrogen tetroxide gas.
8. Solid diboron trioxide reacts with water to form boric acid (H3BO3) in aqueous solution. Advanced problems:
9. __NH3 + __O2 à __NO + __H2O 10. __C2H6 + __O2 à __H2O + __CO
Balancing Equations -‐
Answers 1. 2Li(s) + Cl2(g) → 2LiCl(s) 2. 4Fe(s) + 3O2(g) → 2Fe2O3(s) 3. 2H2O2 → 2H2O + O2 4. 2KClO3(s) → 2KCl(s) + 3O2(g) 5. P4(s) + 6Cl2(g) → 4PCl3(l) 6. Aluminum metal reacts with oxygen gas to produce
aluminum oxide solid. 4Al(s) + 3O2(g) → 2Al2O3(s) 7. Gaseous nitrogen dioxide decomposes to form
dinitrogen tetroxide gas. 2NO2(g) → N2O4(g) 8. Solid diboron trioxide reacts with water to form boric
acid (H3BO3) in aqueous solution. B2O3(s) + 3H2O(l) → 2H3BO3(aq)
9. 4NH3 + 5O2 à 4NO + 6H2O 10. 2C2H6 + 5O2 à 6H2O + 4CO
§ 3. Aqueous Hydrogen peroxide decomposes to produce water and oxygen gas.
§ § § 4. Solid sulfur burns in the presence of oxygen to form sulfur
dioxide gas. § § § 5. Write the balanced synthesis reaction showing the
production of Magnesium nitride from its elements. § § § 6. Solid Iron (III) sulfide is produced from its solid elements.
Write the balanced equation for this reaction.
Title a paper: “Ch 8.1 bookwork” Read ch 8.1 pg 260-275 Answer: Pg. 274 “practice” 1. a-c and Section Review # 1-2, 4-5 And pg 275 #1-2
Lab Safety Review 1. What is the most important rule in the lab? 2. When using a Bunsen burner, what
important safety precautions do you need to take? (min of 3)
3. What can you do to avoid skin contact with any chemicals?
4. If you do accidently get a chemical on you, what should you do?
Ch 8:contniued
ClIF H BrON Diatomic Elements: mnemonic devise
Cl2, I2, F2, H2, Br2, O2, N2
Don’t forget:
5 Types of Chemical Reactions
1. Synthesis 2. Decomposition 3. Single Replacement 4. Double Replacement 5. Combustion
1. Synthesis
§ 2 or more substances combine into one single product
§ Examples: ú Mg (s) + O2 (g) à MgO (s) ú K + Cl2 à KCl ú Cu + S à CuS
Ex: Write the balanced synthesis reaction showing the production of Magnesium nitride from its elements. Ex: Solid Iron (III) sulfide is produced from its solid elements. Write the balanced equation for this reaction
2. Decomposition § The break down of a single substance into 2 or
more products § Examples
ú HgO (s) à Hg (l) + O2 (g) ú H2SO4 (aq)à H2 (g) + S (s) + O2 (g) ú HI à H2 + I2
§ Ex: Write the formula showing the decomposition of hydrobromic acid (HBr) into the diatomics hydrogen gas and bromine liquid
§ Ex: When electricity is applied water as a catalyst, it forces the decomposition of it into diatomic gases of hydrogen and oxygen. Write the balanced equation for this reaction
https://www.youtube.com/watch?v=mamoT11TEV4
3. Single Replacement § One element replaces a 2nd in a compound.
ú Metals displace metals, non-‐metals displace non-‐metals
ú Hydrogen is the exception (acts like a metal)
§ Examples ú Zn + Cu(NO3)2 à Cu + Zn(NO3)2 ú Br2 + NaI à I2 + NaBr ú Zn + H2SO4 à H2 + ZnSO4
Would the following reaction occur??
§ CaCl2 + Na à NaCl + Ca § Will Na displace Ca???
ú Why? ú Why not?
Activity Series: show how reactive an element is.
Pg 286 -‐a more reactive element will replace a less reactive element
Will it react? If so, what is the product?
1. Zn + H2O(l) à 2. Sn + O2 à 3. Cd + Pb(NO3)2 à
4. Cu + HCl à 5. Will solid iron and Lead (II)
nitrate react in a single replacement reaction? If so, write the balanced chemical formula for this reaction.
Cd(NO3)2 + Pb
SnO or SnO2
No reaction
No reaction
4. Double Replacement § 2 elements (metals/+ ions) switch partners. § Examples
ú Na2S + Cd(NO3)2 à CdS + NaNO3 ú NaCN + H2SO4 à ú Ca(OH)2 + HCl à HOH + CaCl2
HOH = Water
+ → + https://www.youtube.com/watch?v=opY3FLrPTa4
HCN + Na2SO4
Write and Balance
1. In a double replacement reaction sodium hydroxide (NaOH) and iron (III) nitrate react. Write the balanced formula for this reaction.
2. Aqueous barium nitrate and aqueous phosphoric acid (H3PO4) react to produce barium phosphate precipitate and aqueous nitric acid (HNO3).
5. Combustion Reaction
§ When a compound or element is burned (in the presence of oxygen)
§ Energy in the form of heat and light is produced
§ Hydrocarbons are often the other reactant. ú Complete combustion products are always CO2 and H2O
ú Incomplete combustion products are typically C (soot), CO gas and H2O
https://www.youtube.com/watch?v=UygUcMkRy_c
Examples of Combustion Rxns
§ C6H6 + O2 à CO2 + H2O (benzene) § CH4 + O2 à CO2 + H2O (methane) Ex: Write a balanced equation for the complete combustion of glucose (C6H12O6).
1. 2SO2 + O2 à 2SO3 2. Al2(SO4)3 + 3Ca(OH)2 à 2Al(OH)3 + 3CaSO4 3. 2C2H2 + 5O2 à 4CO2 + 2H2O 4. Mg + 2AgNO3 à Mg(NO3)2 + 2Ag 5. 3Ba(NO3)2 + 2H3PO4 à Ba3(PO4)2 + 6HNO3 6. Mg(ClO3)2 à MgCl2 + 3O2 7. 2Be + O2 à 2BeO 8. 2Al + 3CuSO4 à Al2(SO4)3 + 3Cu 9. 2PbO2 à 2PbO + O2 10. 2C2H6 + 7O2 à 4CO2 + 6H2O
What type of chemical reaction is each of the following?
1. 2SO2 + O2 à 2SO3 2. Al2(SO4)3 + 3Ca(OH)2 à 2Al(OH)3 + 3CaSO4 3. 2C2H2 + 5O2 à 4CO2 + 2H2O 4. Mg + 2AgNO3 à Mg(NO3)2 + 2Ag 5. 3Ba(NO3)2 + 2H3PO4 à Ba3(PO4)2 + 6HNO3 6. Mg(ClO3)2 à MgCl2 + 3O2 7. 2Be + O2 à 2BeO 8. 2Al + 3CuSO4 à Al2(SO4)3 + 3Cu 9. 2PbO2 à 2PbO + O2 10. 2C2H6 + 7O2 à 4CO2 + 6H2O
1. S 2. DR 3. C 4. SR 5. DR 6. D 7. S 8. SR 9. D 10. C
What type of chemical reaction is each of the following?
Pg 286
Label the type of reaction: 1. 2Be + O2 à 2BeO 2. HI à H2 + I2 3. Br2 + NaI à I2 + NaBr 4. Al2(SO4)3 + 3Ca(OH)2 à
2Al(OH)3 + 3CaSO4 5. CH4 + O2 à
Will it react? If so, write the products 6. ZnCl2 + Ag à 7. Al2(SO4)3 + Ca à 8. Na + O2 à
Warm up
Complete the reaction… § Pb(OH)4 + NaCl à
ú ppt??? § Pb + NaCl à § Are you sure about that answer??? § AgNO3 + MgCl2 à
ú ppt? § KOH à
§ Go to www.creative-‐chemistry.org.uk/gcse/revision/equations/03.htm
§ You will complete at least 20 problems.
§ Sulfuric acid and powdered sugar § https://www.youtube.com/watch?v=ed2AbvQ6ZrQ
Bozeman: § https://www.youtube.com/watch?v=yS8noHTIJ_E
Predicting Precipitates
§ Precipitate: Liquid + Liquid = Solid Cloudy ú Solubility determines formation ú Solubility chart
§ Soluble means NO precipitate will form!
Will a precipitate form?? Write the products first to determine.
Na2 CO3 + Ba (NO3)2 à
H2SO4 + Pb(OH)2 à
We will change seats, but not today. Start a new warm up paper:
1/6/15
Name Per, Row Warm-‐ups #1
1. 2.
Saving paper is always good!
_/__/15
1. What did you do well in Chemistry class last semester?
2. What was something that was hard for you? 3. Set one goal for yourself for this semester in
chemistry class. Read the article “peeing in the pool…” 4. How does your chemistry knowledge help you understand this article? 5. What elements do you think make up cyanogen chloride? Thrichloramine?
Warm up
1. What did you do well in Chemistry class last semester?
2. What was something that was hard for you? 3. Set one goal for yourself for this semester in
chemistry class.
Reminders/ thing to do § Grades from last semester are final, you are starting with a clean slate!
§ Need a notebook, red pen, and calculator ú Can continue using the same notebook, if you have enough room (this is recommended)
§ Clean out your binder/ backpack! (store stuff at home if you want)
§ Keep your final study guide! ú Use it to reference material you might forget!