Chemical reaction · Web viewChapter 7Chemical Reactions I Chemical reactions and chemical equations A. Chemical reactions - Word equation reactants products arrow What evidence do

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


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


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


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.


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)


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


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-


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


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


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:


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 – ___________________


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


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:


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.


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


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


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


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


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

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Chemical reaction · Web viewChapter 7Chemical Reactions I Chemical reactions and chemical equations A. Chemical reactions - Word equation reactants products arrow What evidence do