Chemical Reactions

Chemical reaction

• a chemical change

• bonds of reactants are broken and bonds of product are formed

reactants products(yield or make)

• when some chemicals come into contact with each other, they break apart, join, or rearrange to form new chemicals (always to become more stable)

Evidence of Chemical Rxn

• change in color (unexpected)

• change in temperature

• change in smell

• change in taste

• formation of a precipitate (appears cloudy)

• production of a gas (bubbles)

• production of heat, light, sound

Chemical equations

• shorthand representations of chemical reactions

H2 + O2 H2O

(skeleton equation)

Parts of a chemical equation . . .

• Reactants the elements or compounds that enter into a reaction

• Products are the elements or compounds that are formed as a result of a chemical reaction

• Arrow means yields, produces or forms

reactants products

yield

Formula Equation

2 H2 (g) + O2 (g) 2 H2O (l)

• includes states of matter – (s) – solid– (l) – liquid– (g) – gas– (aq) – aqueous

• chemical equation must be balanced

Word equation

hydrogen gas and oxygen gas form liquid water

2 H2 (g) + O2 (g) 2 H2O (l)

Types of Chemical Reactions

1. Synthesis

2. Decomposition

3. Double Replacement

4. Single Replacement

5. Combustion

1. Synthesis

A + B AB

• two or more substances react to form a single product

• example:

2 H2 (g) + O2 (g) 2 H2O (l)

2. Decomposition

AB A + B

• a single compound breaks down into two or more substance

• example:

2 H2O (l) 2 H2 (g) + O2 (g)

3. Single Replacement

A + BC AC + B

• the atoms of one element replace the atoms of another element in a compound

• example:

Zn (s) + Cu(NO3)2 (aq) Zn(NO3)2 (aq) + Cu (s)

4. Double Replacement

AB + CD AD + CB

• metal cations exchange position between two compounds (dissolved in water)

• example:

AgNO3(aq) + NaCl (aq) AgCl (aq) + NaNO3(aq)

5. Combustion

reactant(s) + O2 product(s)

• oxygen combines with a substance and releases energy (heat & light)

• example:

CH4 (g) + 2 O2 (g) CO2 (g) + 2 H2O (l)

What is the purpose of balancing chemical equations?

• The Law of Conservation of Mass states that matter is neither created nor destroyed during a chemical reaction. Therefore, when writing a chemical equation, the reactants must be equal to the products. So you must add any necessary coefficients to show that matter is conserved.

METAL ACTIVITY SERIES

• During a Single Replacement reaction, a metal will not always replace another metal. This is because metals differ in their reactivities.

MOSTACTIVE

FrLiRbKCaNaMgZnFeNiSnPbCuAgPtAu

LEASTACTIVE

• For example: Francium (Fr) is the most active metal on the table. It will replace (or kick out) any other metal. – NOTE: it’s the highest on the Activity Series list.

• So in the reaction below, the Fr metal with replace the Fe in the iron (II) chloride, resulting in pure iron metal as a product.

2 Fr + FeCl2 2 FrCl + Fe

A Metal Activity Series helps you determine if a reaction will occur.

Au + FeCl2 no reaction

* gold is one of the least active metals, so it will not be able to replace (kick out) the iron metal, and the reaction will not take place.

2 Al + 3 FeCl2 2 AlCl3 + 3 Fe

* Al is more reactive than iron, so it will replace (kick out) the iron metal, and the reaction will take place.

Write out and balance the following

• Sulfur solid reacts with iron solid to form solid iron(III) sulfide.

Magnesium metal reacts with hydrochloric acid to form

magnesium chloride solution and hydrogen gas.

Oxygen gas reacts with solid copper metal to form copper(II)

oxide solid.

Oxygen gas reacts with hydrogen gas to form liquid water.

Hydrogen gas and aluminum chloride solution are produced when solid aluminum is reacted

with hydrochloric acid.

Answer Key

• 3S (s) + 2Fe(s)------> Fe2S3(s)

• Mg(s) + 2HCl(aq)------> MgCl2(aq) + H2(g)

• O2(g) + 2Cu(s)------> 2CuO(s)

• 2H2(g) + O2(g)------> 2H2O(l)

• 2Al(s) + 6HCl(aq)------> 3H2(g) + 2AlCl3(aq)

Try the followingWrite out the formula and balance.

• Dinitrogen pentoxide gas in the presence of a platinum catalyst and high enough temperature forms nitrogen gas and oxygen gas.

• Sulfur solid reacts with iron solid to form solid iron(III) sulfide.

• Hydrogen gas and iron(III) oxide powder react to form liquid water and solid iron powder.

• Magnesium metal reacts with hydrochloric acid to form magnesium chloride solution and hydrogen gas.

• Magnesium sulfide solid and hydrochloric acid react to form hydrogen sulfide gas and magnesium chloride solution.

Key

• 2N2O5(g)------> 2N2(g) + 5O2(g)

• 3S (s) + 2Fe(s)------> Fe2S3(s)

• 3H2(g) + Fe2O3(s)------> 3H2O(l) +2Fe(s)

• Mg(s) + 2HCl(aq)------> MgCl2(aq) + H2(g)

• MgS(s) + 2HCl(aq)------> MgCl2(aq)+ H2S(g)

Finding Formula Mass

• H3PO4

• AlCl3

• K2C4H4O6

• N2O5

• K3SO4

• Nd2O3