Transcript Chemical Reactions

CHEMICAL REACTIONS
MATTER IS ALWAYS CHANGING
• Physical change – the chemical composition of matter does
not change
• Chemical change – chemical composition of matter is not
constant
• Chemical reaction- When a substance undergoes a
chemical change and forms a new substance
IF YOU MIX TWO THINGS TOGETHER
HOW DO YOU KNOW A CHEMICAL
REACTION HAS OCCURRED?
INDICATORS THAT A CHEMICAL
CHANGE HAS OCCURRED
• Gas produced (bubbles)
• Energy change
• Exothermic
• Endothermic
• Light
• Precipitate is formed – precipitate is an insoluble solid formed from
combining two aqueous solutions
• Permanent color change
• pH change
WRITING CHEMICAL EQUATIONS
• Reactants
products
• Reactants – what you start with
• Products – new substances formed
SYMBOLS FOR REACTIONS
•
•
•
•
•
•
•
•
•
•
+ separates 2 reactants or 2 products
(s) solid
(l) liquid
(g) gas
(aq) aqueous – solid dissolved in a liquid
usually water
(c) crystal
 precipitate produced
 gas produced
Δ
energy is needed
 yields or produces- separates reactants from products
WRITING CHEMICAL EQUATIONS
• Ex: A (aq) +
reacts with
B (g)
C (s)
yields/produces
+
D
(aq)
SYMBOLS FOR REACTIONS
•
A catalyst is a substance that speeds up the
reaction but is not used up in the reaction
•
• identified above the yield sign
H2 O 2
KMnO4
H2 + O 2
PRACTICE WRITING CHEMICAL
EQUATIONS
• Write the chemical equation for the following reactions
1. Zinc metal reacts with hydrogen chloride to produce aqueous zinc
chloride and hydrogen gas
2. Aqueous solutions of sodium iodide and silver nitrate yield silver iodide
precipitate and aqueous sodium nitrate
BALANCING CHEMICAL
EQUATIONS
• Remember the Law of Conservation of Matter/Energy?
• We need to balance the equations in order to satisfy
this……
EXAMPLE : BUILDING A BICYCLE
11.1
BALANCING CHEMICAL
EQUATIONS
• To write a balanced chemical equation, first
write the skeleton equation. Then use
coefficients to balance the equation so that
it obeys the law of conservation of mass.
RULES FOR BALANCING
EQUATIONS:
• Write correct skeleton formula
• Determine number of atoms of each element of reactants and products.
COUNT POLYATOMIC ION AS A SINGLE UNIT if it appears unchanged on both
sides of the equation
• Balance elements one at a time by using coefficients-NEVER change
subscripts
• Begin with the easiest elements first
• Check both sides to see if they match
• Make sure coefficients are in the lowest possible ratio
REMEMBER DIATOMICS!!
• When you write the skeleton equation, remember these elements must be
written as 2 atoms when they are not involved in a compound….
• Br2 I2 N2 Cl2 H2 O2 F2
TYPES OF REACTIONS
TYPES OF CHEMICAL REACTIONS
• Synthesis (combination)
• Decomposition
• Single Replacement
• Double Replacement
• Combustion
1. SYNTHESIS
• Synthesis (composition, combination)
reaction
• two or more substances react to form a
single new substance.
A + B  AB
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) 
2. Decomposition
reaction
• a single compound breaks down into
two or more simpler products.
• AB  A + B
DECOMPOSITION
REACTIONS
Rules for 2.
Decomposition
Reactions:
• All binary compounds (ex: MgCl2) will
break down into their elements
• All carbonates (CO32-) break down into
oxide and carbon dioxide
• Chlorates (ClO3-) break down into
binary salt and oxygen
• Bases (OH group) and compounds with
an H and an O will break down into
water and an oxide
–
3. Single Replacement
• one element replaces a second element in a
compound.
M + AB 
MB + A
N + AB 
AN + B
4. COMBUSTION REACTIONS
•Combustion reactions occur when a fuel
reacts with oxygen gas, which produces heat!
Fuel + O2 (+ Heat)  Product
• Combustion reactions
• Cx H y + O 2 
CO2
C3H8(g) +
5O2

+
H 2O
3CO2 + 4H2O + heat
5. DOUBLE REPLACEMENT
(PRECIPITATION)
• Double replacement- also known as
precipitation reaction, (and sometimes
neutralization reaction)
AB + CD  AD + CB
DOUBLE REPLACEMENT
• If a double replacement reaction involves an acid
and a base, then the double replacement reaction
is known as a NEUTRALIZATION reaction
• Acid + base
salt + water
• How do you know if it’s an acid and a base??
ACIDS AND BASES
• Acids – release hydrogen ions (H+) in water
• Ex: HCl hydrochloric acid
• Bases – releases hydroxide (OH-) in water
• Ex: NaOH sodium hydroxide
SO IN A NEUTRALIZATION
REACTION…
• HCl
+
NaOH
Remember that this is a type of double replacement
PRACTICE
sulfuric acid neutralizes a solution of potassium
hydroxide
• 1.
• UH OH! What is the formula for sulfuric acid?
• Hope you studied your polyatomics !
NAMING ACIDS AND BASES
• Bases
• Metal keeps its name, hydroxide
• Ex : NaOH
• sodium hydroxide
NAMING ACIDS AND BASES
• Acids
• Binary acids
•
hydrogen + nonmetal
=
nydro _______- ic acid
Ternary acids
hydrogen + - ite polyatomic
=
_____________ - ous acid
hydrogen + - ate polyatomic
=
_____________ - ic
acid
NAMING ACIDS AND BASES
• Acids
• Ex: what is the formula for sulfuric acid ?
• Ex: what is the formula for nitrous acid ?
SOME PROPERTIES OF ACIDS
 Produce H+ (as H3O+) ions in water (the hydronium
ion is a hydrogen ion attached to a water molecule)
 Taste sour
 Corrode metals
 Electrolytes
 pH is less than 7
 Litmus “ends up “ red ( blue turns red, red stays red)
SOME COMMON BASES
NaOH
sodium hydroxide
KOH
potassium hydroxide
Ba(OH)2
barium hydroxide
Mg(OH)2
magnesium hydroxide
Al(OH)3
aluminum hydroxide
SOME PROPERTIES OF BASES
 Produce OH- ions in water
 Taste bitter, chalky
 Are electrolytes
 Feel soapy, slippery
 pH greater than 7
 Litmus “ends up” blue (red turns blue, blue stays
blue)
The pH Scale
Strong
Weak
Weak
Strong
1 2 3 4 5 6 7 8 9 10 11 12 13 14
BASES
ACIDS
Neutral
PH OF COMMON SUBSTANCES
WHAT IS PH?
• “p” in pH stands for either potential or power
• If more H3O+ in solution than OH- it’s an acid
• If more OH- than H3O+ then it’s a base
• If equal amounts of H3O+ and OH- then it’s neutral
BUFFER
• Buffer is a solution that resists changes and can
control pH when an acid or base is added.
• a buffer consumes excess hydrogen ions or
hydroxide ions which determine the pH
• Made of aqueous weak acid and one of its salts
• Ex: hydrogen carbonate and carbonate ions –
controls the pH of blood at a pH of 7.4