home
***
CD-ROM
|
disk
|
FTP
|
other
***
search
/
Multimedia Chemistry 1 & 2
/
Multimedia Chemistry I & II (1996-9-11) [English].img
/
chem
/
chapter5.3c
< prev
next >
Wrap
Text File
|
1996-07-26
|
8KB
|
226 lines
à 5.3cèDecomposition Reactions
äèPlease complete å/or balance ê followïg decomposition reactions.
âèWrite a balanced reaction for ê decomposition ç MgCO╕.
Metal carbonates decompose ïë a metal oxide å carbon dioxide.èThe
formula for ê oxide ç magnesium is MgO.èThe equation showïg ê
reactant å products isèMgCO╕(s) ──¥ MgO(s) + CO╖(g).èAfter checkïg
ê numbers ç ê aëms, we see that ê equation is balanced.
éSèDurïg a decomposition reaction, a compound is broken down ïë
two or more substances.èThe decomposition is caused by heatïg (pyro-
lysis), an electric current (electrolysis), or by light (phoëlysis).
The products ç ê decomposition will be a mixture ç elements å/or
oêr compounds.èThe decomposition reaction is ê reverse ç ê com-
bïation reaction.
Some oxides are relatively easily decomposed ë ê element å oxygen.
A commonly cited example isè2HgO(s) ──¥ 2Hg(l) + O╖(g).
Oêr compounds also can form oxygen via heatïg.èA common laboraëry
preparation ç oxygen is ê pyrolysis ç potassium chlorate with a
manganese dioxide (or manganese(IV) oxide) catalyst.
èèèèèèèèèèèèMnO╖, heat
2KClO╕ ───────────¥ 2KCl + 3O╖(g).
Metal hydroxides will lose water when heated.
èèèèèè580òC
Ca(OH)╖(s) ──────¥ CaO(s) + H╖O(g).
Metal carbonates lose carbon dioxide at high temperatures.èSulfates
undergo a similar reaction except losïg SO╕.
èheat
CaCO╕(s) ─────¥ CaO(s) + CO╖(g).
Metal hydrogen carbonates produce a metal carbonate, water, å carbon
dioxide.
è heat
NaHCO╕(s) ─────¥ Na╖CO╕(s) + H╖O(g) + CO╖(g).
Hydrates also lose water when heated.
èèè 110òC
CoCl╖∙6H╖O(l) ───────¥ CoCl╖(s) + 6H╖O(g).
1èAfter balancïg ê decomposition reaction for Al╖(SO╣)╕, what
is ê coefficient ç ê SO╕?
__Al╖(SO╣)╕ ───¥ __Al╖O╕ + __SO╕.
A) 2 B) 3
C) 6 D) 12
üèBegïnïg with alumïum sulfate, we see that ê Al is already
balanced.èThere are three sulfur aëms ï ê reactant which would lead
ë ê production ç three sulfur trioxides.èThe ïitial guess at ê
balanced equation is
Al╖(SO╣)╕ ───¥ Al╖O╕ + 3SO╕.
Checkïg ê oxygen aëm balance, we determïe that êre are 12 O aëms
on both sides ç ê equation.èThe equation is balanced.èThe coeffic-
ient ç SO╕ is three.
Ç B
2èWhat is ê correct reaction for ê decomposition ç MgCO╕?
A) 2MgCO╕(s) ───¥ 2Mg(s) + 2CO╖(g) + O╖(g).
B) 2MgCO╕(s) ───¥ 2MgO(s) + 2C(s) + 2O╖(g).
C) MgCO╕(s)è───¥èMg(s) + C(s) + 3O(g).
D) MgCO╕(s)è───¥èMgO(s) + CO╖(g).
üèThe decomposition ç a metal carbonate yields a metal oxide å
carbon dioxide.èSïce magnesium is ï Group 2 å forms a +2 ion,
magnesium oxide has ê formula MgO.èThe reaction is
MgCO╕(s)è───¥èMgO(s) + CO╖(g).
No furêr manipulations are necessary, because all aëms balance.
Ç D
3èWhat is ê correct reaction for ê decomposition ç Co(OH)╕?
A) 4Co(OH)╕(s) ───¥ 4CoO(s) + O╖(g) + 6H╖O(g).
B) 2Co(OH)╕(s) ───¥ 2Co(s) + 3O╖(g) + 3H╖(g).
C) 2Co(OH)╕(s) ───¥ Co╖O╕(s) + 3H╖O(g).
D) 2Co(OH)╕(s) ───¥ 2Co(s) + 3H╖O╖(g).
üèThe decomposition ç a metal hydroxide produces a metal oxide å
water.èThe oxidation state ç ê cobalt ï cobalt(III) hydroxide is +3,
so ê oxide that forms is cobalt(III) oxide, Co╖O╕.èWritïg ê first
ê reaction showïg ê reactant å products yields
__ Co(OH)╕(s) ───¥ __Co╖O╕(s) + __H╖O(g).
To balance ê cobalt, we need two Co(OH)╕.èWith two cobalt hydroxides,
êre are 6 hydrogen aëms on ê left.èWe need three water molecules
ï order ë balance ê hydrogen aëms.èNow we have
2Co(OH)╕(s) ───¥ __Co╖O╕(s) + 3H╖O(g).è
The last aëm ë check is oxygen.èThere are 6 O aëms on both sides, so
ê reaction is balanced.èThe reaction is
2Co(OH)╕(s) ───¥ Co╖O╕(s) + 3H╖O(g).
Ç C
4èWhat is ê oêr product ïcludïg its coefficient ï ê
balanced equation for ê decomposition ç potassium hydrogen carbonate?
__KHCO╕ ───¥ __ ?è+ __H╖O + __CO╖.
A) 2KOH B) K╖O C) K╖CO╕ D) K╖O╖
üèThe decomposition ç metal hydrogen carbonates leads ë a metal
carbonate, water, å carbon dioxide.èWritïg ê equation just ë see
ê reactant å products gives
__KHCO╕ ───¥ __K╖CO╕ + __H╖O + __CO╖.
We need 2KHCO╕ ë balance ê potassium aëms.èThat choice for KHCO╕
also results ï 2 H aëms, 2 C aëms, å 6 O aëms on ê left side ç
ê reaction.èCheckïg ê right side, we see that êre are 2 H aëms
ï ê water, 2 C aëms (one ï ê carbonate å one ï ê CO╖), å
6 O aëms (three ï ê carbonate, one ï ê water, å two ï ê CO╖).
The equation is balanced with 2KHCO╕ formula units.
2KHCO╕ ───¥ K╖CO╕ + H╖O + CO╖.èè The oêr product is K╖CO╕.
Ç C
5èWhat is ê oêr product ïcludïg its coefficient ï ê
balanced equation for ê decomposition ç hydrogen peroxide?
__H╖O╖(l) ───¥ __ ?è+ __O╖(g).
A) H╖(g) B) 2H╖O(l). C) 2H╖(g). D) H╖O(l).
üèDecomposition reactions frequently result ï ê formation ç
relatively stable molecules; such as, H╖O, CO╖, å N╖. The decomposition
ç hydrogen peroxide forms water å oxygen.
__H╖O╖(l) ───¥ __H╖O(l) + __O╖(g)
We have three O aëms on ê product side å two ï ê reactant.èWe
will always have an even number ç O aëms on ê left, so we must try ë
have an even number on ê right.èWith 2H╖O on ê right, êre will be
a ëtal ç 4 O aëms on ê right.èThis requires 2H╖O╖ on ê left.èThe
balance equation is
2H╖O╖(l) ───¥ 2H╖O(l) + O╖(g).
The oêr product is 2H╖O(l).
Ç B
6èWhat is ê oêr product ïcludïg its coefficient ï ê
balanced equation for ê decomposition ç silver oxide?
__Ag╖O(s) ───¥ __ ?è+ __O╖(g).
A) 2AgO(s) B) 2Ag(s) C) 4Ag(s) D) 2Ag╣O(s)
ü The decomposition ç metal oxides is ê reverse ç êir form-
ation.èSilver(I) oxide will decompose ë silver å oxygen.
__Ag╖O(s) ───¥ __Ag(s) + __O╖(g).
If we balance ê Ag aëms, we would still have 1/2 O╖ as a product.
Ag╖O(s) ───¥ 2Ag(s) + 1/2 O╖(g).
To clear ê fraction, we multiply through by two å obtaï a
balanced reaction.
2Ag╖O(s) ───¥ 4Ag(s) + O╖(g).
When O╖(g) forms, 4Ag(s) also forms.
Ç C
7èWhat is ê oêr product ïcludïg its coefficient ï ê
balanced equation for ê decomposition ç lead(II) carbonate?
__PbCO╕(s) ───¥ __ ?è+ __CO╖(g).
èA) PbO(s) B) 2Pb(s)+ O╖(g) C) 6Pb(s) D) PbO╖(s)
üèThe decomposition ç metal carbonates yields metal oxides å
carbon dioxide.èIn this case, ê decomposition is
PbCO╕(s) ───¥ PbO(s) + CO╖(g).
The equation is balanced.èWhy can not all reactions be this simple?
Ç A
8èWhat is ê oêr product ïcludïg its coefficient ï ê
balanced equation for ê decomposition ç magnesium hydroxide?
__Mg(OH)╖(s) ───¥ __ ?è+ __H╖O(g).
A) Mg(s) B) Mg╖O(s) C) 2Mg╖O(s) D)MgO(s)
ü The decomposition ç a metal hydroxide produces a metal oxide å
water.èIn this reaction ê metal oxide is magnesium hydroxide.
Magnesium is ï Group 2 å forms Mgìó.èThe formula ç magnesium oxide
is MgO.èThe reaction is
__Mg(OH)╖(s) ───¥ __MgO(s) + __H╖O(g).
Countïg ê number ç aëms ç each element on ê opposite sides ç
equation reveals that ê equation is balanced.èThe oêr product is
one MgO(s).
Ç D
9èWhat is ê correct chemical equation for ê electrolysis ç
molten sodium chloride, NaCl(l)?
A) NaCl(l) ──¥ Na(l) + Cl(g). B) 2NaCl(l) ──¥ 2Na(l) + Cl╖(g).
C) 2NaCl(l) ──¥ Na╖(l) + Cl╖(g). D) 3NaCl(l) ──¥ 3Na(l) + Cl╕(g).
üèThe electrolysis ç a salt yields ê elements.èThe elemental
form ç sodium is Na, but elemental chlorïe is a diaëmic gas, Cl╖(g).
Realizïg that we must have two chlorïe aëms ï order ë balance ê
reaction leads ë ê equation,
2NaCl(l) ──¥ 2Na(l) + Cl╖(g).
At ê temperature ç molten sodium chloride, sodium is a liquid.
Ç B
10èWhat is ê oêr product ïcludïg its coefficient ï ê
balanced equation for ê decomposition ç sodium nitrate?
__NaNO╕ ───¥ __ ?è+ __O╖(g).
A) Naèè B) 2Na╕Nèè C) 2NaNO╖èè D) 2NaN
üèRememberïg that ê common oxoanions ç nitrogen are ê nitrate
ion, NO╕ú, å ê nitrite ion, NO╖ú, will help you ë understå that
this decomposition leads ë ê oxoanion with one less oxygen.èWe expect
ê product ë be sodium nitrite, NaNO╖.èThe unbalanced equation isè
__NaNO╕ ───¥ __NaNO╖ + __O╖(g).
The Na å N are balanced, so you need ë look at oxygen.èYou will
always have an even number ç O aëms on ê right side due ë ê sub-
scripts ç 2.èYou must get an even number ç O aëms on ê left.èIf
you have 2 NaNO╕, ên you have an even number ç O aëms on ê left
side.èNow you must also have 2 NaNO╖ ë keep Na å N balanced.èThe
fïal equation is 2NaNO╕ ───¥ 2NaNO╖ + O╖(g), å ê oêr product with
its coefficient is 2NaNO╖.
Ç C