Physical Science Week 13
Day 1 - 2 | Day 3 | Day 4 | Lab | Vocabulary Test

vocabulary for the week
  • Chemical reaction
  • Precipitate
  • Reactant
  • Product
  • Synthesis
  • Decomposition
  • Single displacement
  • Double displacement
  • Combustion

Combinations of Matter

link to a local webpage What are coefficients?

(ps lab 065)
When a chemical reaction occurs, there is always a change in the properties and energy content of the substances involved. There is a change in both the physical and chemical properties as substances are changed into new substances.
At least one of these should be obvious when a chemical reaction takes place:

Color change - new substances might reflect different colors of light.
Heat change - the container may get hotter or colder.
Gas produced - bubbles or smoke may be observed.
Precipitate formed - an insoluble solid might form in a liquid.


In order for a chemical reaction to take place, the reactants must have the ability to form chemical bonds. These bonds are formed by the valence electrons of the reactant atoms. If substances are brought together whose valence electrons do not match together to complete the Octet Rule, there will be no chemical reaction.

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.
Reactants Products
Law of conservation of mass:

During a chemical reaction, atoms are neither created nor destroyed. This means that the number of atoms remains constant throughout the reaction. Since the number of atoms doesn't change, the mass must remain constant as well.

There are times when mass might appear to change during a chemical reaction. If you experience this during an experiment, be sure to remember the law of conservation of mass.

The change in mass must be accounted for in a way other than destroying or creating atoms.

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Chemical Engineer
 Chemical reaction types:

We will study these five general types of reactions: synthesis, decomposition, single displacement, double displacement, and combustion. Once you know these reaction types, you will be able to look at the reactants of a reaction and predict what products will be formed.

Two examples are given for each of the reaction types below. You might notice that the same number of atoms of each element are found on both sides of the reaction arrow. This is accomplished by the added numbers in front of some of the chemical formulas known as coefficients. They are added to "balance" the equation. You will learn how to balance equations next week.link to a local webpage

Synthesis: two simple substances combine to form a more complex one.

Examples of synthesis reactions:
Decomposition: a complex substance breaks down into two simple substances.
Examples of decomposition reactions:
Single displacement: a single element replaces an element in a compound.
Examples of single displacement reactions:
Double displacement: two different atoms in two different compounds exchange places.
Examples of double displacement reactions:
Combustion: a hydrocarbon (molecule containing only carbon and hydrogen atoms) reacts with oxygen. The products of combustion are always carbon dioxide and water.
Examples of combustion reactions:

Go to chemistry class for more about chemical reactions.link to a local webpage

Test Your Concept Understanding:

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. C4H10 + O2 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

Day 3

link to a local webpage What does the oxidation number of an element tell you?

link to a local webpage with useful information Now that you know the general types of chemical reactions, you can predict what the products of a reaction will be when you are given the reactants. You will need to be able to write the correct formulas for the reactants by using the oxidation numbers of elements link to a local webpage and polyatomic ions. link to a local webpage

 

Example #1: Predict the products of this reaction.     H + O

1. What type of reaction is it? synthesis
2. Move the chemical symbols to
represent a synthesis reaction. 		H + O HO
3. Add subscripts to make the oxidation numbers
of the elements in the product equal to zero. 		H + O H2O This equation is not balanced.
You will do that next week.

 

Example #2: Predict the products of this reaction.     BaCl2 + Al2(SO4)3
1. What type of reaction is it? double displacement
2. Move the chemical symbols to represent
a double displacement reaction. 		BaCl2 + Al2(SO4)3 AlCl + BaSO4
3. Add subscripts to make the oxidation numbers
of the elements in the product equal to zero. 		BaCl2 + Al2(SO4)3 AlCl3 + BaSO4

Sample problem: Write the correct formulas for the products of Al + CaO  

In-class Assignment 133:
This assignment must be turned in by the end of class today to receive credit.
Scoring criterialink to a local webpage

Write the correct formulas for the products formed in these reactions:

  1. Mg + O2
  2. Ag + H2S
  3. Ca(NO3)2 + Na2CO3
  4. C3H8 + O2
  5. Al2O3
  6. K + H2O (hint: think of water as HOH)
  7. Ba + FeBr2
  8. AgNO2 + NaCl
  9. H2O
  10. Ca3(PO4)2 + H2SO4

Day 4

Just because substances come in contact with each other does not mean a chemical reaction must occur. Predicting whether a reaction will take place is not always easy. You have learned something about using the periodic table to determine how chemically "active" an element is. In general, if one element is more active than another, the more active element will replace the less active element in a compound - thus a chemical reaction will take place.

The table below lists metals in order of reactivity, or tendency to react. A metal on the table will usually displace any below it on the table.
Most Reactive

Potassium
Calcium
Sodium
Magnesium
Aluminum
Zinc
Iron
Tin
Lead
Hydrogen
Copper
Mercury
Silver
Gold

Least Reactive

In-class Assignment 134:
This assignment must be turned in by the end of class today to receive credit.
Scoring criterialink to a local webpage

Use the table to predict which of these balanced single displacement reactions can and cannot occur:

  1. Zn + CaCl2 Ca + ZnCl2
  2. 6Na + Fe2O3 2Fe + 3Na2O
  3. 3Sn + Al2O3 3SnO2 + 4Al
  4. Mg + 2HCl MgCl2 + H2
  5. 2AgNO3 + Cu 2Ag + Cu(NO3)2
  6. 2Ag + 2HCl 2AgCl + H2
  7. Pb(NO3)2 + 2Cu 2CuNO3 + Pb
  8. MgCl2 + 2K 2KCl + Mg
  9. SnCO3 + Au AuCO3 + Sn
  10. 2Fe + 3Na2O 6Na + Fe2O3


Physical Science

 

 

 

 

 

 

 

type of reactions:

  1. synthesis
  2. single displacement
  3. single displacement
  4. double displacement
  5. combustion
  6. decomposition
  7. double displacement
  8. double displacement
  9. single displacement
  10. double displacement

 

 

 

 

 

 

 

   

 

Coefficients are the large numbers in front of chemical formulas in a chemical equation.
Coefficients indicate the number of molecules. Think of this as the ratio of the molecules involved in the chemical reaction.

 

 

 

 

 

 

 

   

 

The oxidation number of an element indicates the number of electrons gained or lost when forming compounds.
A positive oxidation number means the atom looses electrons and a negative oxidation number means the atom gains electrons. predicting products:

  1. MgO
  2. AgS + H2
  3. NaNO3 + CuCO3
  4. CO2 + H2O
  5. Al + O2
  6. KOH + H2
  7. BaBr2 + Fe
  8. NaNO3 + AgCl
  9. H2 + O2
  10. CaSO4 + H3PO4