TYPES OF TYPES OF CHEMICAL CHEMICAL REACTIONSREACTIONS

TYPES OF TYPES OF CHEMICAL CHEMICAL REACTIONSREACTIONS

To react or not to react? To react or not to react? THAT is the question!THAT is the question!

• Chemical changes are a result of chemical reactions.

• All chemical reactions involve a change in substances and a change in energy.

• Neither matter or energy is created or destroyed in a chemical reaction---only changed.

• Synthesis Reaction• Decomposition Reaction• Single Displacement Reaction• Double Displacement Reaction• Activity Series of Metals

• TYPES OF CHEMICAL REACTIONS

SYNTHESIS REACTION• In a synthesis reaction two or more simple

substances combine to form a more complex substance.

• The reaction through the equation: reactant + reactant -------> product A + B -------> AB

• For example, simple hydrogen gas combined with simple oxygen gas can produce a more complex substance—water!

• The chemical equation for this synthesis reaction is: 2H2 + O2 2H2O

• In the cartoon, the skinny bird (reactant) and the worm (reactant) combine to make one product, a fat bird.

Synthesis Reactions

• metal + oxygen metal oxide 4Fe(s) + 3O2(g) 2Fe2O3(s)

• nonmetal + oxygen nonmetal oxide S(s) + O2(g) SO2(g)

• metal oxide + water metallic hydroxide MgO(s) + H2O(l) 2Mg(OH)2(s)

• nonmetallic oxide + water acid SO3(g) + H2O(l) H2SO4(aq)

• metal + nonmetal salt 2Na(s) + Cl2(g) 2NaCl(s)

Rusting of Iron

DECOMPOSITION REACTION

• In a decomposition reaction a more complex substance breaks down into its more simple parts.

• One reactant yields 2 or more products. Basically, synthesis and decomposition reactions are opposites. reactant -------> product + product

AB -------> A + B

• For example, water can be broken down into hydrogen gas and oxygen gas.

• The chemical equation for this decomposition reaction looks like:

2H2O 2H2 + O2

Explosions

• The explosion of a dynamite is an example of a decomposition reaction. When suitably activated, a highly exothermic reaction occurs in which large amounts of gaseous products form.

• Nitroglycerin, which can be activated merely by shaking, decomposes as follows:

4C3H5(NO3)3(l) 6N2 (g) + 12CO2(g) + 10H20(g) + O2(g)

• The egg (the reactant), which contained the turtle at one time, now has opened and the turtle (product) and egg shell (product) are now two separate substances.

Decomposition Reactions

• Metallic carbonates, when heated, form metallic oxides and CO2(g).

CaCO3(s) CaO(s) + CO2(g).

• Most metallic hydroxides, when heated, decompose into metal oxides and water.

Ca(OH)2(s) CaO(s) + H2O(g).

• Some oxides, when heated, decompose.

2HgO(s) 2Hg(l) + O2(g)

• Some acids, when heated, decompose into nonmetallic oxides and water.

H2SO4(s) H2O(l) + SO3(g)

SINGLE DISPLACEMENT REACTION

• In a single displacement reaction a single uncombined element replaces another in a compound.

• A metal replaces a metal and a non metal replaces a non metal

• Two reactants yield two products. reactant + reactant ---------> product + product

AB + C -------> AC + B

• For example when zinc combines with hydrochloric acid, the zinc replaces hydrogen.

• The chemical equation for this single replacement reaction looks like:

Zn + 2HCl ZnCl2 + H2

• Notice, the guy in the orange shirt steals the date of the other guy. So, a part of one of the reactants trades places and is in a different place among the products.

Single Displacement Reactions

• Replacement of a metal in a compound by a more active metal.

Fe(s) CuSO4(aq) + FeSO4(aq) + Cu(s)

• Replacement of hydrogen in water by an active metal.

Mg(s) + H2O(aq) MgO4(aq) H2(g)

• Replacement of hydrogen in acids by active metals.

Zn(s) + 2HCl(aq) ZnCl2(aq) + H2(g)

• Replacement of nonmetal by a more active nonmetal.

Cl2(g) + 2NaBr(aq) 2NaCl(aq) + Br2(g)

DOUBLE REPLACEMENT REACTION

• In a double displacement reaction parts of two compounds switch places to form two new compounds.

• Two reactants yield two products.

reactant + reactant ---------> product + product

AB + CD -------> AC + BD

• For example when silver nitrate combines with sodium chloride, two new compounds--silver chloride and sodium nitrate are formed because the sodium and silver switched places.

• The chemical equation for this double replacement reaction looks like

AgNO3 + NaCl AgCl + NaNO3

• Why do you take a tablet when you have an upset stomach?

• Calcium carbonate reacts with the hydrochloric acid in your stomach. This is shown in this equation:

CaCO3 + 2HCl CaCl2 + H2CO3

Metal Activity Series

Metal Metal Ion Reactivity

Lithium Potassium Calcium Sodium Magnesium Aluminum Manganese Zinc Chromium Iron Lead Copper Mercury Silver Platinum Gold

Li+ K+ Ca2+ Na+ Mg2+ Al3+ Mn2+ Zn2+ Cr2+, Cr3+ Fe2+, Fe3+ Pb2+ Cu2+ Hg2+ Ag+ Pt2+ Au+, Au3+

Most Reactive - - - - - - - - - - - - - - Least Reactive

• A metal can replace metals listed below it in the activity series, but not above. For example, sodium is highly active and thus able to replace hydrogen from water:

– 2 Na (s) + 2 H2O (l) → 2 NaOH (aq) + H2 (g)

• The reactivity series determines qualitatively characteristics such as the reactions with water, air and acids as demonstrated above. However it is defined by the nature of the metals in single displacement reactions.

• When a metal in elemental form is placed in a solution of a metal salt it may be, overall, more energetically feasible for this "elemental metal" to exist as an ion and the "ionic metal" to exist as the element. Therefore the elemental metal will 'displace' the ionic metal over time, thus the two swap places. Only a metal higher in the reactivity series will displace another.