Chemical Reactions

Using Everyday Equations

Every minute of the day chemical reactions are taking place both in and around you.

What makes something a chemical reaction?

Products

“ ” means “yields” or “reacts to produce.”

Reactants

A chemical reaction involves one or more substances,the reactants, changing into one or more substances,the products.

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Chemical reactions can be described many ways. One is by using a word equation.

A word equation is an equation where reactants and products are represented by words.

Example:

methane + oxygen carbon dioxide + water

Word equations, while useful, are cumbersome. To better describe a reaction, writing the formulas is used.

A chemical equation uses formulas of reactants (on the left) separated by an arrow from products (on the right).

Example:

Fe + O2 Fe2O3

(Skeleton equation)

- does not indicate the relative amounts of reactants and products

Most often symbols are used to describe the state (i.e., gas, solid, etc.) of each substance

Types of Reactions

• The four types of chemical reactions we will talk about are:

1. Synthesis reactions

2. Decomposition reactions

3. Single displacement reactions

4. Double displacement reactions

• You need to be able to identify the type of reaction and predict the product(s)

Steps to Writing Reactions• Some steps for doing reactions

1. Identify the type of reaction

2. Predict the product(s) using the type of reaction as a model

3. Balance it

Don’t forget about the diatomic elements! (BrINClHOF) For example, Oxygen is O2 as an

element.

In a compound, it can’t be a diatomic element because it’s not an element anymore, it’s a compound!

1. Synthesis reactions• Synthesis reactions occur when two

substances (generally elements) combine and form a compound. (Sometimes these are called combination or addition reactions.)

reactant + reactant 1 product• Basically: A + B AB

• Example: 2H2 + O2 2H2O

• Example: C + O2 CO2

2. Decomposition Reactions• Decomposition reactions occur when a

compound breaks up into the elements or in a few to simpler compounds

• 1 Reactant Product + Product

• In general: AB A + B

• Example: 2 H2O 2H2 + O2

• Example: 2 HgO 2Hg + O2

3. Single Displacement Reactions

• Single Replacement Reactions occur when one element replaces another in a compound.

• A metal can replace a metal (+) OR a nonmetal can replace a nonmetal (-).

• element + compound product + product A + BC AC + B (if A is a metal) ORA + BC BA + C (if A is a nonmetal)

(remember the cation always goes first!)

When H2O splits into ions, it splits intoH+ and OH- (not H+ and O-2 !!)

We have looked at several reactions:Fe + CuSO4 Cu + Fe2(SO4)3

Li + H2O LiOH + H2

Such experiments reveal trends. The activity series ranks the relative reactivity of metals.It allows us to predict if certain chemicals will undergo single displacement reactions when mixed: metals near the top are most reactive and will displacing metals near the bottom.Q: Which of these will react?

Fe + CuSO4 Ni + NaCl Li + ZnCO3 Al + CuCl2

Cu + Fe2(SO4)3

Yes, Fe is above Cu

NR (no reaction)

No, Ni is below Na

Zn + Li2CO3Cu + AlCl3

Yes, Al is above Cu

KNaLiCaMgAlZnFeNiSnPbH

CuHgAgAu

Yes, Li is above Zn

H is the only nonmetal listed. H2 may be displaced from acids or can be given off when a metal reacts with H2O (producing H2 + metal hydroxide). The reaction with H2O depends on metal reactivity & water temp. Q: will Mg react with H2O?

KNaLiCaMgAlZnFeNiSnPbH

CuHgAgAu

cold H2O

hot H2O

steam

acid

NR

A: No for cold, yes if it is hot/steamMg + H2O

H2 + ZnCl2Complete these reactions:Al + H2O(steam) Cu + H2O Ca + H2SO4 Na + H2O

H2 + Mg(OH)2

H2 + Al(OH)3

H2 + CaSO4

H2 + NaOH

Q: Zn + HCl

• All metals will have a specific place in the activity series. For simplicity, only the most common metals are shown.

• The metals near the top of the activity series are more reactive because their valence electrons are more easily removed.

• On tests and exams the activity series may appear as K, Na, … Ag, Au; you must remember that K is reactive, Au is not.

• If the valence of a metal is not indicated in the question, use its most common valence (in bold on your periodic table) to determine the correct chemical formula.

Other Activity Series Information

4. Double Displacement Reactions

• Double Replacement Reactions occur when a metal replaces a metal in a compound and a nonmetal replaces a nonmetal in a compound

• Compound + compound product + product

• AB + CD AD + CB

Double Displacement Reactions

• Think about it like “foil”ing in algebra, first and last ions go together + inside ions go together

• Example:

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

• Another example:

K2SO4(aq) + Ba(NO3)2(aq) KNO3(aq) + BaSO4(s) 2