Balancing and reaction types

1. Chemical Reactions

have two parts:

Reactants= the substances you start with

Products= the substances you end up with

The reactants will turn into the products.

Reactants->Products

A reaction can be described several ways:

#1. In asentenceevery item is a word

Copper reacts with chlorine to form copper (II) chloride.

#2. In aword equationsome symbols used

Copper + chlorine->copper (II) chloride

#3. In achemical equationonly chemical equations are used

Cu + Cl 2 ->CuCl 2

(s) after the formula = solid: Fe (s)

(g) after the formula = gas: CO 2(g)

(l) after the formula = liquid: H 2 O (l)

(aq) after the formula = dissolved in water, anaqueous solution: NaCl (aq)is a salt water solution

the arrow-> separates the reactants from the products(arrow pointstoproducts)

Read as: reacts to form or yields

The plus sign + means and

used after a product indicates a gas has beenproduced :H 2

used after a product indicates a solid has beenproduced :PbI 2

double arrowindicates a reversible reaction (more later)

shows that heat is supplied to the reaction

is used to indicate a catalyst is supplied(in this case, platinum is the catalyst)

A substance that speeds up a reaction, without being changed or used up by the reaction.

Enzymesare biological or protein catalysts in your body.

All chemical equations are adescriptionof the reaction.

A skeleton equation uses formulas and symbols to describea reaction

but doesnt indicate how many; this means they are NOT balanced

Solid iron (III) sulfide reacts with gaseous hydrogen chloride to form iron (III) chloride andhydrogen sulfide gas.

Nitric acid dissolved in water reacts with solid sodium carbonate to form liquid water and carbon dioxide gas and sodium nitrate dissolved in water.

Solid iron (III) sulfide reacts with gaseous hydrogen chloride to form iron (III) chloride andhydrogen sulfide gas.

FeS (s)+ HCl (g) ->FeCl 2(s)+ H 2 S (g)

Nitric acid dissolved in water reacts with solid sodium carbonate to form liquid water and carbon dioxide gas and sodium nitrate dissolved in water.

HNO 3 (aq)+ Na 2 CO 3(g) ->CO 2(g)+ H 2 O (l)

Fe (s)+ O 2(g) ->Fe 2 O 3(s)

Cu (s)+ AgNO 3(aq) ->Ag (s)+ Cu(NO 3 ) 2(aq)

NO 2(g) N 2(g)+ O 2(g)

According to the Law of Conservation of Mass:atoms arent created or destroyed in a chemical reaction , they are just rearranged.

All the atoms westart within the reactants we mustend up with in the products(meaning: balanced!)

A balanced equation has the same number of each elementon both sidesof the equation.

Assemble thecorrect formulasfor all the reactants and products, using + and ->

Count the number of atoms of each type appearing on both sides

Balance the elementsone at a timeby addingcoefficients(the numbers in front) where you need more -save balancing the H and O until LAST!

(hint: I prefer to save O until theverylast)

Double-Checkto make sure it is balanced.

Neverchange asubscriptto balance an equation (You can only changecoefficients )

If you change the subscript (formula) you are describing a different chemical.

H 2 O is a different compound than H 2 O 2

Neverput a coefficient in themiddleof a formula; they must go only in thefront

2 NaCl is okay, but Na 2 Cl is not.

_AgNO 3+ _Cu->_Cu(NO 3 ) 2+ _Ag

_Mg + _N 2 ->_Mg 3 N 2

_P + _O 2 ->_P 4 O 10

_Na + _H 2 O->_H 2+ _NaOH

_CH 4+ _O 2 ->_CO 2+ _H 2 O

2 AgNO 3+ _Cu->_Cu(NO 3 ) 2+2 Ag

3 Mg + _N 2 ->_Mg 3 N 2

4 P +5 O 2 ->_P 4 O 10

2 Na +2 H 2 O->_H 2+2 NaOH

_CH 4+2 O 2 _CO 2+2 H 2 O

There are probably millions of reactions.

We cant remember them all, but luckily they will fall into several categories.

We will learn: a) the5 major types .

We will be able to: b)predictthe products .

For some, we will be able to: c) predict whether or not they willhappen at all .

How?We recognize them by theirreactants

also called Combination Reactions

2 substances combine to make one compound

the general equation is :A+B->AB

Ca+ O 2 -> Ca O element + element

S O 2+ O 2 -> S O 3 compound + element

CO 2+ H 2 O->H 2 C O 3 compound + compound

We can predict the products, especially if thereactants are two elements .

Mg + N 2 -> _______

Ca + Cl 2 ->

Fe + O 2->(assume iron (II) oxide is the product)

Al + O 2->

Remember that thefirst stepis to write thecorrect formulasyou can still change thesubscriptsat this point, but not later while balancing!

Then balanceby changing thecoefficientsonly

one reactantbreaks apart into two or more elements or compounds.

the general equation is :AB->A + B

H 2 OH 2+ O 2

CaCO 3 CaO + CO 2

CuSO 4 5H 2 O CuSO 4+ 5H 2 O

2NaHCO 3(s) Na 2 CO 3(s) +H 2 O (l) +CO 2(g)

Note thatenergy(heat, sunlight, electricity, etc.) is usually required

We can predict the products if it is a binary compound (which means it is made up of only two elements)

It breaks apart into the elements:

A reaction where an element displaces another element in a compound, producing a new compound and an element

A metal will replace a cation (metal or H)

A non-metal will replace an anion (non-metal)

Zn (s) +2 HCl(aq) ->ZnCl 2 (aq)+ H 2 (g)

zinc metal and hydrochloric acid react to form zinc chloride and hydrogen gas in this single-displacement reaction.

One element replaces another

the reaction follows the form of:compound + element-> compound + element

Reactants must bean element and a compound.

Products will be a different element and a different compound.

Na+ KCl -> K + NaCl(cations switched)

F 2+ LiCl -> LiF + Cl 2 (anions switched)

Metals will replace other metals (and they can also replace hydrogen)

Zn (s) +2 HCl(aq) ->ZnCl 2 (aq)+ H 2 (g)

Cu (s)+ 2AgNO 3-> 2Ag (s)+ Cu(NO 3 ) 2

Think of water as:HOH

Metals replace the first H, and then combines with the hydroxide (OH).

2Na(s)+ 2H 2 O (l) ->2 NaOH (aq) +H 2(g)

We can even tellwhether or nota single displacement reaction will happen:

More active elementreplacesless active

TheActivity Series of Metalslists metals (and hydrogen) in order of activity.

Elements higher on the list replaces those lower on the list.

Lithium

Potassium

Calcium

Sodium

Magnesium

Aluminum

Chromium

Nickel

Hydrogen

Bismuth

Copper

Mercury

Silver

Platinum

Metals can replace other metals, provided they are above the metal they are trying to replace(for example, zinc will replace lead)

Metals above hydrogen can replace hydrogen in acids.

Metals from sodium upward can replace hydrogen in water.

Fe + CuSO 4 ->

Pb + KCl->

Al + HCl->

Two compounds switch parts to make two new compounds

the reaction is:

compound + compound -> compound + compound

NaOH +FeCl 3 ->

The positive ions change place.

NaOH +FeCl 3 -> -> Fe +3 OH - +Na +1 Cl -1

= NaOH +FeCl 3 -> -> Fe (OH) 3+ Na Cl

Have certain driving forces , or reasons

Willonlyhappen if one of the products:

a) doesnt dissolve in water and forms a solid (a precipitate ), or

b) is agasthat bubbles out, or

c) is amolecular compound(which will usually be water).

assume all of the following reactions actually take place:

CaCl 2+ NaOH->

CuCl 2+ K 2 S->

KOH + Fe(NO 3 ) 3 ->

(NH 4 ) 2 SO 4+ BaF 2 ->

NaOH (aq) + HCl (aq) ->H 2 O (l) +NaCl (aq)

Look at thereactants :

E + EORC + C= Synthesis

C = Decomposition

E + C = Single displacement

C + C= Double displacement

H 2+ O 2-> ->

H 2 O-> ->

Zn + H 2 SO 4 -> ->

HgO-> ->

KBr + Cl 2 -> ->

AgNO 3+ NaCl-> ->

Mg(OH) 2+ H 2 SO 3-> ->

Combustion is a fast reaction of a substance with oxygen to make compounds calledoxides .

the general equation is :

fuel + oxygen->oxides + energy

the three things that must be present for combustion to happen are:

oxygen

spark / heat

What is the main purpose for which fuels are burned around the world?

The following equations show what happens when different carbon-based fuels are burned.

C (s) +O 2(g) ->CO 2(g) +energy

CH 4(g) +2O 2(g) ->CO 2(g) +2H 2 O+energy

ethanol CH 3 CH 2 OH (l) +O 2(g) ->CO 2(g) +3H 2 O (l)

C 6 H 12 O 6(s)+ 6O 2(g) ->6CO 2(g)+ 6H 2 O (g)+ energy

Some fuels do not contain carbon.

The products are oxides of each element in the fuels.

Mg (s) +O 2(g) ->MgO (s)

Cu (s) +O 2(g) ->CuO (s)

H 2(g) +O 2(g) ->H 2 O (l)

P 4(s)+ 5O 2(g) ->P 4 O 10(g)

S (s)+ O 2(g) ->SO 2(g)

As you see, many combustion reactions may also be classified as synthesis.

Describes a reaction

Must be balanced in order to follow the Law of Conservation of Mass

Can only be balanced by changing thecoefficients.

Hasspecial symbolsto indicate the physical state, if a catalyst or energy is required, etc.

Come in 5 major types.

We can tell what type they are by looking at the reactants.

Single Replacementhappens based on theActivity Series

Double Replacementhappens if one product is: 1) a precipitate (an insoluble solid), 2) water(a molecular compound) , or 3) a gas.

Many reactions occur in water- that is, inaqueous solution

When dissolved in water, many ionic compounds dissociate, or separate, into cations and anions

Now we are ready to write anionic equation

Example(needs to be a double replacement reaction)

AgNO 3+ NaClAgCl + NaNO 3

1. this is thefull balanced equation

2. next, write it as anionic equation by splitting the compounds into their ions:

Ag 1++ NO 3 1-+ Na 1++ Cl 1-

AgCl + Na 1++ NO 3 1-

Note that the AgCl did not ionize, because it is a precipitate

3.simplifyby crossing out ions not directly involved (called spectator ions)

Ag 1++ Cl 1- AgCl

This is called thenet ionic equation

Lets talk about precipitates before we do some other examples

Insoluble salt = a precipitate[note Figure 11.11, p.342 (AgCl)]

Generalsolubility rulesare found:

Table 11.3, p. 344 in textbook

Reference section - page R54 (back of textbook)

Lab manual Table A.3, page 332

Yourperiodic table handout

Balancing and reaction types

Education

Transcript of Balancing and reaction types