Chemical reactions

References:

Chemical equations

•Define a chemical reaction

•Chemical equation describes the reaction:

reactants -------> products

Parts of a chemical reaction:

  Reactants - •Substances that interact with each other. •On the left side of the arrow in a chemical equation.

  Products - •New substances formed during a reaction. •On the right side of the arrow in at a chemical equation.

Word and formula equations

Type and number of atoms

Word and formula equations

Steps involved in writing a 'balanced' equation for a chemical reaction:

1. Experimentally determine reactants and products:

“Hydrogen reacts with oxygen to make water”

2. Write 'un-balanced' equation using formulas of reactants and products

H2 + O2 H2O

3. Write 'balanced' equation by determining coefficients that provide equal numbers of each type of atom on each side of the equation (generally, whole number values)

Balancing equations

Law of conservation of mass

The law

Law of conservation of mass

The total mass of these beakers does not change despite a chemical reaction having taken place.

Antoine Lavoisier is also known as “The Father of Modern Chemistry”. He was a French nobleman prominent in the histories of chemistry and biology. He stated the first version of the Law of Conversion of mass, recognized and named oxygen in 1778 and also recognized and named hydrogen in 1783.

Skill builder p.145

STM assignment p.146 – make a ppt from 3 slides and present it

Pracs p. 148

Types of reactions

SYNTHESIS REACTION

Two or more simple substances combine to form a more complex substance.

The chemical equation for this synthesis reaction looks like:                                   

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

To visualize a synthesis reaction look at the following cartoon:

                                                    

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

Examples of synthesis reactions:

•2Na + Cl2 →    2NaCl

•4Fe + 3O2 →    2Fe2O3

DECOMPOSITION REACTIONIn a decomposition reaction a more complex substance breaks down into its more simple parts. Basically, synthesis and decomposition reactions are opposites.

The chemical equation for this decomposition reaction looks like:                                   

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

To visualize a decomposition reaction look at the following cartoon:

                                                                           

In this cartoon 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.

Examples of decomposition reactions: •2H2O →    2H2 + O2

•H2CO3 →   H2O + CO2

Raisin lava lamp

• p. 150

Combination reaction

What is combination reaction?

In a single replacement reaction a single uncombined element replaces another in a compound.  

To visualize a single replacement reaction look at the following cartoon:

                                                      

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

Examples of single displacement reactions: •Zn + 2HCl   → ZnCl2 + H2

•2Na + 2H2O   →   2NaOH + H2

SINGLE REPLACEMENT REACTION

DOUBLE REPLACEMENT REACTIONIn a double replacement reaction parts of two compounds switch places to form two new compounds. Two reactants yield two products. 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:                                                         reactant + reactant ---------> product + product

To visualize a double replacement reaction look at the following cartoon:

                                             

 Notice how the first guy exchanged hats with the second guy, so they are both wearing each other's hat.Examples of double displacement reactions: •MgCO3 + 2HCl    MgCl2 + H2CO3

•2KCl + Pb(NO3)2    2KNO3 + PbCl2

Precipitation reactions

Two soluble reactants combine to form an insoluble product, called precipitate.

Using text / tables p.151-153 make it prac lesson – base on p.160 prac for summative prac

OPTION:

Dissolving an ionic substance

What happens with the ions and with the water molecules?

Ionic substances and their names – Table 5.2.1 and 5.2.2. p. 152

Naming ionic compounds

Predicting precipitation – (use skill builder p.153)

Identify the "type" for each reaction below: 1.Ca + O    CaO 2.Br + LiI    LiBr + I 3.Al + Fe(NO3)2    Al(NO3)3 + Fe

4.MgO + HCl    MgCl2 + H2O

5.C4H10O2    CO2 + H2O

6.NH4NO2    NH3 + H2O

7.(NH4)3PO4 + Sr(OH)2    Sr3(PO4)2 + NH4OH

8.H2SO4 + NaOH    Na2SO4 + H2O

9.Zn + AgNO3    Zn(NO3)2 + Ag

10.CuNO3 + KCl    KNO3 + CuCl

Oxidation and reduction reactions

Oxidation reactions

Flames shoot from the liquid methane-liquid oxygen engine during the 103-second test firing (Image: NASA/MSFC/T Leibold)

Write the chemical reaction:

Reduction reactions

Copper oxide + carbon ???

Write the chemical equation + explain what happens with oxygen

Redox reactions and electrons

http://seniorphysics.com/chem/eei.html

Make photos of the experiment, write the observations and explanation

• After 1 minute the two solutions have different Cu2+ concentrations shown by the different intensities of blue colour. This means more

Zn has reacted in one than the other.

Fixed ions

In metals: Chaotic movement of electrons

No movement of charged particles

METALSIONIC SUBSTANCES

In solution there are ions

- 2 e-

Zinc atom Zinc ion

Electricity

• Need moving charges

• Electrons in metals could move

• Ions in solutions could move

• THEREFORE, the metals and the solutions of the ionic substances can conduct electricity

Metal displacement reactions. Activity series

Activity series

Extraction of metals

Read p.156 and write the important information

Electrolysis of NaCl

In solution in beginning of reaction

2

2

11

21

12

H e H

Cl Cl e

Na OH NaOH

In solution end of reaction

2

NaCl Na Cl

H O H OH

Electrolysis of NaCl

Molten NaCl

2

1

11

2

Na e Na

Cl Cl e

NaCl Na Cl

Metal ores

Less reactive metals are found uncombined in the earth's crust.Because of this the inactive metals were among the first to be discovered - gold is found in ancient tombs, the stone age was followed by the bronze age (copper).More reactive metals have to be extracted from ores. Ores are naturally-occurring compounds of metals.

Extracting Metals from Ores

Extracting of a metal from its ore is an example of reduction.

Heat alone

When silver oxide (Ag2O) is heated, it decomposes to form silver metal and oxygen gas.

2(Ag+)2O2-  → 4Ag  +  O2Ag+  +  e-  →  Ag        (reduction) Some metals can be obtained from metal oxides by heat alone.These metals lie towards the bottom of the reactivity series.

Heating with some other substanceCarbonMetals like copper or lead can be extracted from their oxides by heating with carbon

powder.Cu2+O2- + C  → Cu + CO2

Cu2+  +  2e-  →  Cu              (reduction) 

Carbon monoxideMetals like copper, lead, iron and zinc are extracted from their oxides in a blast

furnace (see later). 

HydrogenMetals like copper and lead can be obtained from their oxides by heating in a

stream of hydrogen gas Pb2+O2- + H2  → Pb + H2O

 Pb2+  +  2e-  →  Pb              (reduction) 

These metals that can be extracted from ores by heating with another substance, lie in the middle of the reactivity series.

 ElectricityMetals high up the reactivity series, like aluminium and sodium have to be extracted

using heat and electricity. The metal gains electrons from the negative electrode.Al3+  +  3e-  →  Al               (reduction)

Carbon reductionlow down the furnace coke burns to

form carbon dioxide C  +  O2  →  CO2

further up the furnace the carbon dioxide reacts with more coke

forming carbon monoxideC  +  CO2  →  2CO

this carbon monoxide reduces the iron ore to iron

3CO  +  Fe2O3  →  3CO2  +  2Feor

Fe3+  3e-  →  Fe  (reduction)the molten iron trickles to the bottom of the furnace where it is tapped offlimestone is added to remove acidic

impurities as slag

Pracs p.59-161

5.3. Rate of chemical reactions – only pracs