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Chapter 7 Chemistry 101/105 page 1 of 19
Chapter 7 Chemical Reactions
I Chemical reactions and chemical equations
A. Chemical reactions -
Word equation
reactants
products
arrow
What evidence do we have of a chemical change?
B. Chemical equation- represent ____________ what is taking place during
reaction; an expression in which __________________________ are used to represent a chemical reaction,
Formula equation:
state of each substance: as subscripts in parenthesis
Chapter 7 Chemistry 101/105 page 2 of 19
II Balancing Chemical Equations
A. Background
B. Balanced equation
Law of Conservation of Mass –
C. How to balance
1. Write correct ____________ or ____________________ for each reactant or product
2. Place _____________________ (number in front) in front of the compounds to make the same number of atoms of each element on both sides of the equation.
_____________ Change subscripts (this changes compound!!!)
a. Start with _______atom (just choose one, but not one that is in multiple compounds)
b. Choose next atom and __________ on equation
Chapter 7 Chemistry 101/105 page 3 of 19
c. Check next atom and continue to build on equation
3. Verify the atom count
Reactant Product
Equation is not finished until it’s balanced!!!
4. Make sure coefficients are reduced to their ___________________ values.
5. Include the ____________________ (if necessary) in parenthesis
Example:aluminum sulfate and barium nitrate react to form aluminum nitrate and barium sulfate
Chapter 7 Chemistry 101/105 page 4 of 19
III What a balanced reaction tells us
A. Items it does not tell us1.
2. 3.
B. Proportions or ___________
____ atoms + _____molecule ______formula units
____ dozen atoms + _____dozen molecules ______dozen formula units
_____ million atoms + _____million molecule ______ million formula units
_____ mol atoms + ______mol molecule _____ mol formula units
IV Summary for balancing reactions
1. Number of atoms of _____________ of element is the _______________ in the reactants and the products. (conservation of mass)
2. _________________ does not change since atoms do not change mass, the mass of the reactants equal the mass of the products
3. The total numbers of ________________ on each side of the equation may or may not be equal.
Chapter 7 Chemistry 101/105 page 5 of 19
V. Types of chemical reactions
A. Combustion reactionsWhen a substance is burned in _________-(consuming ____________)
1. substance is burned in air (consuming oxygen)
general equation
ex:
2. A substance containing carbon and hydrogen
______________________ and sometimes oxygen burn in air (consuming oxygen) to produce CO2 and water. Usually gives off lots of heat Fuel
general equation
ex: CH4 + 2 O2 2 H2O + CO2 methane, gas for houseex: C2H5OH+ 3 O2 3 H2O + 2 CO2 ethanol
respiration – “burning food” burning carbohydrates
ex: C6H12O6+ 6 O2 (s) 6 H2O (l) + 6 CO2 (g)
Chapter 7 Chemistry 101/105 page 6 of 19
B. Synthesis (combination) reactions one element with another to produce a compound
general equation
ex: 2H2 + O2 2 H2O ex: 2 H2O + CO2 2 H2CO3
C. Decomposition reactions
A single substance is broken down into two or more simplesubstances (compounds or elements)
General equation:
ex: 2 HgO2 Hg + O2 - heat above arrow
ex: Na2CO3 CO2 + Na2O
D. Single Replacement Reactions (always redox)
General equation:
one substance replaces another in a compound
ex: Mg + 2 HCl H2 + MgCl2
ex: Cu(s) + 2 AgNO3(aq) Cu(NO3)2 (aq) + 2 Ag (s)
some combustion rxn are single replacement
ex: respiration
______________________________ of elements
ranks elements in order of their reducing ability in aqueous solution
Any element higher in the activity series will react with the ionsof any element lower in the activity series
Chapter 7 Chemistry 101/105 page 7 of 19
Cu is above silver so Cu(s) + AgNO3 (aq)
but gold is below silver Au(s) + 3 AgNO3 (aq)
Fluorine is above bromine so F2 + 2 NaBr (aq)
but iodine is below bromine so I2 + NaBr (aq)
E. Double replacement reactions (metathesis) never redox
General Equation
ions in compounds AB and CD switch partners, usually takes place in an aqueous solution
1. Neutralization of an acid and a base
ex:
2. Formation of ________________________
ex:
3. Formation of a ____________
ex:
VI. Aqueous Solutions
A. Definitions
1. _____________________________ – a homogenous mixture of a substance in water.
When a substance is dissolved, it is not a chemical reaction, only a phase change
2. ____________________– separate into ions when dissolved, usually ionic compounds
ex: NaCl separates into Na+ and Cl-
Chapter 7 Chemistry 101/105 page 8 of 19
3. ____________________ – a substance whose aqueous solution
contains __________ and therefore conducts
_________________
a. _________________ electrolytes – compounds that dissociate to a large extent into ions when dissolved in water, (70-95%)
ex: NaCl
b. ____________ electrolytes – compounds that dissociate to only a small extent , only partially ionized in waterex: acetic acid
CH3COOH(l) H+ (aq) + CH3COO- (aq)
in solution, less than 1 % of acetic acid dissociates, at equilibrium, at any given moment some acetic acid molecules are dissociating while some acetate ions and hydrogen ions are recombining to form acetic acid
4. ___________________________ - a substance whose aqueous
solution does not contain ions and does ____________________
ex: most molecules, covalent compounds
5. _____________________________ – a substance that ________ to a significant extent in the solvent
6. ______________________________ – a substance that does ___ dissolve to a significant extent in the solvent
Chapter 7 Chemistry 101/105 page 9 of 19
VII Net ionic equations
A. Background
One chemical (_____________ )is dissolved in water (_____________)
and reacts with another chemical dissolved in water. Both compounds are
dissolved (_________________ separate into individual ions) or are in
______________ solution, therefore the reactions are ________________
B. Aqueous Reactions and net ionic equations
1. Molecular equation (write correct formulas and balance, identify physical states)
2. Total Ionic equation (TIE) (split all aqueous reactants and products)
Since the reaction is in an aqueous solution, the ionic compounds and acid will dissociate.
Actually the Na+ + Cl- are not involved in the reaction, they themselves
are not changed, they are called “_______________________”
3. Net ionic equation (NIE)The reaction would be simplified by removing the spectator ions:
This is the net ionic equation
Chapter 7 Chemistry 101/105 page 10 of 19
VIII. Precipitation Reactions (and other related rxns)
Type of _____________________________ Reactiongeneral equation
_________________ reaction– a reaction in which an insoluble solid forms in a solution during a chemical reaction
__________________– an insoluble solid that forms in a solution during a chemical reaction
________________ – the amount of the solid that will dissolve in a given amount of solvent at a given temperature
Not all ionic compounds are equally soluble. To predict if a double replacement
reaction will go occur, a solid product (________________), a ______________
or a _________________should form.
Driving forces that cause the reaction to occur
Some Solubility Rules: Table 7.2 textbook NO3
- All nitrates are soluble
Cl-, Br-, I- All chlorides, bromides, and iodides are soluble (except Ag+ and Pb2+ compounds)
NH4+ All compounds with the ammonium ion are soluble
SO42- Most sulfates are soluble (except Ba2+ and Pb2+ sulfates)
CO32- All carbonates are insoluble except those of Group I elements
and NH4+.
OH- All hydroxides are insoluble except those of Group I elements and Sr(OH)2 and Ba(OH)2.
All group 1 cations are soluble
Additional rules exist...check your book ex:
Chapter 7 Chemistry 101/105 page 11 of 19
Problems: Write the total ionic and net ionic equations for the following reactions using the solubility rules.
1. Copper I sulfate and barium chloride react in a double replacement reaction.
2. Sodium carbonate and sulfuric acid react to form sodium sulfate and carbonic acid (which decomposes to carbon dioxide and water)
Driving forces
BaSO4 – _____________ CO2 – _______________ H2O – ___________________
Chapter 7 Chemistry 101/105 page 12 of 19
IX Acid –Base reaction (____________________)
Type of _______________________________ rxn
sodium hydroxide and hydrochloric acid react to form sodium chloride and water
molecular equation:
NaOH – base in water dissociates into ___________ and __________
HCl – acid in water dissociates into ________ and _______
Total ionic equation:
__________ - ionic compound formed from a rxn of a acid with a base
(since in an aqueous solution, the salt will dissolve)
Actually the _________ and _________ are not involved in the reaction, they
themselves are not changed, they are called “_________________”
net ionic equation:
a _____________________ is formed, driving force
called ___________________________ because when moles of acid and base
are equal, the solution is not acidic or base but neutral
Chapter 7 Chemistry 101/105 page 13 of 19
X. Exothermic and Endothermic Reactions
A. Heat of reaction
__________________________________ – the amount of heat absorbed
or released in a reaction, this is otherwise known as _________________
(The difference between the amount of energy absorbed in breaking bonds and the energy released by making bonds is called the heat of reaction.)
Energy units
SI unit = ____________ _____________ is more common
or 1 cal = 4.184 j or 1 Cal = 1000 cal = 1 kcal = 4.184 kJ
Calories on food packages (the big C actually means kcal)
B. Exothermic
_______________________ - a process or reaction that ____________
heat to surroundings and has a ______________ H
Products end up with less energy than they started with
The reaction will _____________________________ and release it to surrounding (test tube will feel warm to your hand)
ex: combustion
C. Endothermic
__________________ - a process or reaction that ______________
heat from surroundings and has a______________H
Products end up with more energy than they started with
The reaction will ________________________ from its surrounding (test tube will feel cold to your hand) ex:
Chapter 7 Chemistry 101/105 page 14 of 19
XI. When Reactions Occur
A. For a reaction to occur: (in chap 15 a bit)
1. _________________particles must _________________ with the
____________________________
effective vs. ineffective collisions
solids react more slowly than liquids or gases since they move more freely, if a solid is reacting, the reaction only occurs at surface, when the products fall off the surface, fresh solid is exposed and the reaction continues.....rust
2. ___________________ must take place with ________________ to break appropriate bonds.
If not enough energy, then collisions are like bumper cars and products do not form
ex: tapping glass vs hitting with a hammer
B. Activation energy
1. Between the reactants and the products there is an “energy barrier” that must be climbed. The height of this barrier represents the amount of energy the colliding particles must have for productive collisions to occur.
Chapter 7 Chemistry 101/105 page 15 of 19
2. __________________________________- the amount of energy necessary for reactant to surmount the energy barrier to react, determines reaction rate (It is different for different reaction)
(the minimum energy necessary for the reaction to happen)
Activation energy causes bonds in reactant molecules to break. When the broken bonds form new bonds in the products, energy is released...this causes more reactant bonds to break.
Once reaction is started, enough energy is released to activate other molecules to react and the reaction continues, like the rock over the hump
ex: match, activation energy is provided by rubbing the match head again rough surface, once started, it continues
The size of the activation energy determines the ____________________, a measure of how fast the reaction occur
The ________________ the activation energy, the _______________ the reaction
The ________________ the activation energy, the _______________ the reaction
Chapter 7 Chemistry 101/105 page 16 of 19
Energy Diagrams
Note the size of the activation energy and the size of the energy changes are unrelated
Both reactions are initiated by an increase in energy of the reactants and end with an energy fall
Chapter 7 Chemistry 101/105 page 17 of 19
XII. Effect of temperature, concentration and catalysts on reaction rates
to help reaction over the height of the activation energy some things can be done
A. Temperature
when temperature ______________________, the __________________ of
collisions increase and the __________________ of collisions increase
Remember –temperature is a measure of the kinetic energyRule of thumb- a 10 C increase in temperature doubles reaction ratea 10 C decreases in temperature halves reaction rate: this is why we have refrigerators since rotting is a chemical reaction
B. Concentration
a measure of how many particles of the chemical (whether atoms, molecules or ions) are present in a given volume
if the concentration is ________________, then reactants are more crowded
together and collisions become more ________________ and reactions more likely
Chapter 7 Chemistry 101/105 page 18 of 19
C. Catalysts
_______________________ - a substance that speeds up the rate of the chemical reaction by participating but it itself is unchanged
Catalyst doesn’t affect the energy level of either reactant or products but increases a reaction rate by letting a reaction take place through a pathway of a lower energy barrier
A catalyst ___________________________
ex: catalytic converter on cars....speed up reactions in the exhaust gases to produce less polluting products than would otherwise be released
ex: enzymes – biological catalysts, protein molecules that accelerate chemical like digestion, amylase in mouth breaks down sugars
Chapter 7 Chemistry 101/105 page 19 of 19
Effects of Changes in Reaction Conditions on Rates
Change EffectConcentration Increase in reactant concentration increases rate
Decrease in reactant concentration decreases rateTemperature Increase in temperature increases rate
Decrease in temperature decreases rateCatalyst added Increases reaction rate