1. Unit 8: Chemical Equations
Chapter 10
Chemistry 1K
Cypress Creek High School

2. Table of Contents Chapter 10 10.1: Reactions & Equations
10.2: Classifying Chemical Reactions
10.3: Reactions in Aqueous Solutions

3. 10.1
Reactions & Equations
Chemical Reactions
When a substance undergoes a chemical change, it takes part in a chemical reaction.
After it reacts, it no longer has the same chemical identity.
What are the evidences that a chemical change has occurred? _______________

4. Writing Chemical Equations
10.1
Reactions & Equations
Writing Chemical Equations
In order to completely understand a chemical reaction, you must be able to describe any changes that take place.
A substance that undergoes a reaction is called a reactant.
When reactants undergo a chemical change, each new substance formed is called a product.

5. Chemical Reactions Example
10.1
Reactions & Equations
Chemical Reactions Example
Remember the classic science fair project - the homemade volcano?
It’s done by combining vinegar and baking soda (and some red food coloring for effect).
These substances undergo a chemical reaction, evident by the overflow and bubbles.
This reaction produces three new substances: water, carbon dioxide, and sodium acetate (used in hot packs)
Reaction of baking soda and vinegar:

6. 10.1
Reactions & Equations
Chemical Equations
The simplest way to represent this reaction is by using words
Chemical equations replace chemical names with chemical formulas
Reactants (LEFT)
substances that undergo a reaction
Yield sign (MIDDLE)
represents the change/reaction
Products (RIGHT)
new substances formed in a reaction

7. Writing Equations from Words
10.1
Reactions & Equations
Writing Equations from Words
Write the formula for each reactant and each product.
Your formula MUST be correct.
Remember the diatomic elements H, O, F, Br, I N, Cl. The are written H2, O2, F2, Br2, I2, N2 and Cl2

8. Chemical Equations Practice
10.1
Reactions & Equations
Chemical Equations Practice
What is the chemical equation for the following reactions?
What are the reactants and products?
1) Water and sulfur trioxide combine to form sulfuric acid
2) Potassium chlorite decomposes to form potassium chloride and oxygen
H2O + SO3 → H2SO4
reactants product
KClO2 → KCl + O2
reactant products

9. Chemical Equations States of Matter
10.1
Reactions & Equations
Chemical Equations States of Matter
Some chemical equations indicate the state of matter of the substances (i.e. liquid)
Solid (s) - baking soda
Liquid (l) - water
Gas (g) - carbon dioxide
Aqueous (aq) - vinegar and sodium acetate
Aqueous means the substance is dissolved in water. For example, NaCl(aq) means table salt dissolved in water. This may be the only way the reaction can occur.   

10. Chemical Equations Energy
10.1
Reactions & Equations
Chemical Equations Energy
Energy is either released or absorbed during a chemical reaction. Can be many forms of energy (light, heat, mechanical, chemical, etc).
Endothermic reactions absorb energy.
Energy is a reactant
Can feel cool to the touch

11. Chemical Equations Energy
10.1
Reactions & Equations
Chemical Equations Energy
Energy is either released or absorbed during a chemical reaction. Can be many forms of energy (light, heat, mechanical, chemical, etc).
Exothermic reactions release energy.
Energy is a product
Can feel warm to the touch

12. Chemical Equations Energy
10.1
Reactions & Equations
Chemical Equations Energy
Photosynthesis: plants consume carbon dioxide, water, and light energy (from the sun) and convert it into sugar (glucose), oxygen, and water.
6 CO2(g) + 12 H2O(l) + energy → C6H12O6(aq) + 6 O2(g) + 6 H2O(l)
Cellular Respiration: animals consume sugar (glucose) and oxygen to produce carbon dioxide, water, and chemical energy (ATP)
C6H12O6(aq) + 6O2(g) → 6CO2(g) + 6H2O(l) + energy
These chemical equations are important principles of biology.
Which is endothermic and which is exothermic?

13. Parts of a Reaction Reactants Products Subscript State of Matter
10.1
Reactions & Equations
Parts of a Reaction
Reactants
Products
Subscript
State of Matter
Coefficient
Arrow means “to yield”

14. Law of Conservation of Mass
10.1
Reactions & Equations
Law of Conservation of Mass
The LCM says matter is neither created nor destroyed
The mass of the reactants is always the same as the mass of the products.
The number of atoms of each element is always the same in the reactants and the products.

15. 10.1
Reactions & Equations
LCM
The Law of conservation of matter states that matter cannot be created or destroyed, it can only change forms. Therefore, in a chemical reaction the number of atoms, the mass and the charge must be conserved.
This means it is the same on both sides of the arrow.

16. 10.1
Reactions & Equations
LCM Examples
Hydrogen gas and oxygen gas combine to create water.
2H2 + O2  2H2O
The large numbers, known as coefficients, indicate how many moles of each compound there are. This helps to satisfy the LCM!
They apply to every element in the compound (2H2O means 4 H’s & 2 O’s)
They are the coefficients should be in the lowest whole number ratio
Particles are rearranged, not created or destroyed!

17. LCM Examples 10.1 Reactions & Equations
This should be a review - just count moles of atoms!
How many carbon atoms are conserved? Hydrogen atoms? Oxygen atoms?

18. 10.1
Reactions & Equations
LCM Examples
Calcium chloride and sodium sulfate combine to form calcium sulfate and
sodium chloride. CaCl2 + Na2SO4  CaSO4 + 2NaCl
# atoms in the reactants
# atoms in the products Ca 1 Cl 2 Na S O 4
Total 10
Before and After:
Does the mass change?
Do the number of atoms change?

19. Review of Chemical Equations
10.1
Reactions & Equations
Review of Chemical Equations
Label the following chemical equation:
reactants
products
SnO2(s) + 2H2(g)  Sn(s) + 2H2O(g)
subscript
coefficient
state of matter
yield sign

20. Balancing Chemical Equations
10.1
Reactions & Equations
Balancing Chemical Equations
Remember that atoms don’t change in a chemical reaction; they just rearrange.
The number and kinds of atoms present in the reactants of a chemical reaction are the same as those present in the products.
For a chemical equation to accurately represent a reaction, the same number of each kind of atom must be on the left side of the arrow as are on the right side.
If an equation follows the law of conservation of atoms, it is said to be balanced.

21. Balancing Chemical Equations
10.1
Reactions & Equations
Balancing Chemical Equations
Because the Law of Conservation of Mass (LCM) states that matter is not created or destroyed, the number of atoms of each element must be identical in the reactants and products. This means the chemical equation is balanced.
Example 1:
This equation is balanced because it satisfies the LCM
Writing coefficients is not necessary because each compound has a coefficient of 1
# atoms in the reactants
# atoms in the products H 2 C 1 O 3
Total 6

22. Balancing Chemical Equations
10.1
Reactions & Equations
Balancing Chemical Equations
Example 2:
# atoms in the reactants
# atoms in the products Na 1 2 O 3 4 H C
Total 6 9
This equation is not balanced because it does not satisfy the LCM
Writing coefficients is necessary
So we have to balance the equation…

23. Balancing Chemical Equations
10.1
Reactions & Equations
Balancing Chemical Equations
Example 2 continued:
The process of balancing chemical equations requires trial and error.
You may not alter the subscripts because it changes the substance!
You may only place coefficients in front of the compounds. These act as multipliers to balance the number of atoms.
By placing a 2 in front of NaOH, the equation now satisfies the LCM and is balanced
# atoms in the reactants
# atoms in the products Na 2 O 4 H C 1
Total 9
***Tip: balance hydrogen and especially oxygen last - they often fall into place!

24. Balancing Chemical Equations Practice
10.1
Reactions & Equations
Balancing Chemical Equations Practice
Write a balanced chemical equation for the following reactions. Place coefficients in the blanks. Chemical equations never actually write the coefficient “1”, but for this activity write a number in every blank.
A) ___ K(s) + ___ H2O(l)  ___ H2(g) + ___ KOH(aq)
B) ___ CaCl2(aq) + ___ Na2CO3(aq)  ___ CaCO3(s) + ___ NaCl(aq)
C) ___ N2(g) + ___ H2(g)  ___ NH3(g)

25. 10.1
Reactions & Equations
Question 1
Write a balanced chemical equation for the following reactions, making sure coefficients are in their lowest possible ratio.
Solid potassium reacts with liquid water to produce hydrogen gas and a water solution of potassium hydroxide.
Calcium chloride and sodium carbonate in water solution produce solid calcium carbonate and a water solution of sodium chloride.

26. Classifying Chemical Reactions
10.2
Classifying Chemical Reactions
Classifying Chemical Reactions
Reactions are classified into several categories.
Synthesis A + B  AB
Decomposition AB  A + B
Single Replacement A + BC  AC + B
Double Replacement AB + CD  AD + CB
Combustion CxHy + O2  CO2+ H2O
By recognizing these patterns, you can classify a reaction and make predictions about its products.
Compare these reactions to dancing!

27. 10.2
Classifying Chemical Reactions
Synthesis Reaction
Whenever two or more substances combine to form a single product, the reaction is called a synthesis reaction.
When iron rusts, iron metal and oxygen gas combine to form one new substance, iron (III) oxide.

28. Decomposition Reaction
10.2
Classifying Chemical Reactions
Decomposition Reaction
Whenever a compound breaks down into two or more simpler substances, the reaction is called a decomposition reaction.
When hydrogen peroxide spontaneously decomposes, it becomes water and oxygen gas.
2H2O2(aq)  2H2O(l) + O2(g)

29. Major Classes of Reactions
10.2
Classifying Chemical Reactions
Major Classes of Reactions
In a decomposition reaction, a compound breaks down into two or more simpler substances.
The compound may break down into individual elements, such as when mercury(II) oxide decomposes into mercury and oxygen.
The products may be an element and a compound, such as when hydrogen peroxide decomposes into water and oxygen.
The compound may break down into simpler compounds.

30. Single-Displacement Reaction
10.2
Classifying Chemical Reactions
Single-Displacement Reaction
Whenever one element takes the place of another, the reaction is called a single-displacement reaction.
This reaction will only occur if the more active metal will become part of a compound in the product.
An iron nail soaking in copper (II) sulfate yields iron (II) sulfate and copper

31. Activity Series DECREASING ACTIVITY
10.2
Classifying Chemical Reactions
Activity Series
Most Active Li Rb K Ca Na Mg Al Mn Zn Fe Ni Sn Pb H2 Cu Hg Ag Pt Au
DECREASING ACTIVITY
This feature is found on your handy helper.
Use it to determine whether a single-displacement reaction will occur (react) or not.
Active metals have a low electronegativity. They bond with nonmetals more readily because they are less stable by themselves.
If a very active metal is competing with a less active metal to bond (with a nonmetal or negatively charged polyatomic ion), the more active metal will “win”.
Think of it as a competing suitors who want to date the same girl!
Least Active

32.     Activity Series DECREASING ACTIVITY Pb + MgSO4  PbSO4 + Mg 
10.2
Classifying Chemical Reactions
Activity Series
Most Active
Example #1: Is this combination possible?
Pb + MgSO4  PbSO4 + Mg
Answer: No, because Mg is more active than Pb
Example #2: Is this combination possible?
NaNO3 + K  Na + KNO3
Answer: Yes, because K is more active than Na Li Rb K Ca Na Mg Al Mn Zn Fe Ni Sn Pb H2 Cu Hg Ag Pt Au
DECREASING ACTIVITY      
Least Active

33. Double-Displacement Reaction
10.2
Classifying Chemical Reactions
Double-Displacement Reaction
Whenever two ionic compounds trade cations, the reaction is called a double-displacement reaction.
One of the products will either be water, a gas, or most commonly a precipitate (insoluble in water).
Lead (II) nitrate and potassium iodide form lead (II) iodide and potassium nitrate. Note the yellow precipitate is PbI2.

34. 10.2
Classifying Chemical Reactions
Combustion Reaction
Whenever hydrocarbons combine rapidly with oxygen (usually by fire), the reaction is called a combustion reaction.
The products will be water and carbon dioxide.
Burning methane (CH4) yields water and carbon dioxide
This reaction contributes to our greenhouse gases and global warming.

35. Predicting Products of Chemical Reactions
Class of Reaction
Reactants
Probable Products
Synthesis
Two or more substances
One compound
Combustion
A metal and oxygen]
A nonmetal and oxygen
A compound and oxygen
The oxide of the metal
The oxide of the nonmetal
Two or more oxides
Decomposition
Two or more elements and/or compound
Single-replacement
A metal and a compound
A nonmetal and a compound
A new compound and the replaced metal
A new compound and the replaced nonmetal
Double-replacement
Two compounds
Two different compounds, one of which is often a solid, water, or a gas

36. Identifying Chemical Reactions
10.2
Classifying Chemical Reactions
Identifying Chemical Reactions
Identify each of the following chemical equations as synthesis, decomposition, single-displacement, double-displacement, or combustion reaction. A) B) C)

37. Predicting Chemical Reactions
10.2
Classifying Chemical Reactions
Predicting Chemical Reactions
Steps
Determine what type of reaction is being presented
Write the correct formulas for the product(s)
Balance the equation
Example: CaCl2 + Al(OH)3  ?
Double-displacement reaction
__CaCl2 + __Al(OH)3  __Ca(OH)2 + __AlCl3
3CaCl2 + 2Al(OH)3  3Ca(OH)2 + 2AlCl3

38. Predicting Chemical Reactions Practice
10.2
Classifying Chemical Reactions
Predicting Chemical Reactions Practice
Predict the chemical reaction: NaCl + Ca(OH)2  ?
Predict the chemical reaction: Mg + CuSO4  ?

39. 10.2
Classifying Chemical Reactions
Question 1
Identify each of the following skeleton equations as representing a synthesis reaction, a combustion reaction, both synthesis and combustion, or decomposition reaction.
synthesis;
decomposition

40. Reactions in Aqueous Solutions
10.3
Reactions in Aqueous Solutions
Reactions in Aqueous Solutions
When aqueous solutions that contain ions are mixed, the ions may react in a double-replacement reaction.
The product is typically a solid precipitate, water, or a gas.

41. Reactions in Aqueous Solutions
10.3
Reactions in Aqueous Solutions
Reactions in Aqueous Solutions
To show all of the particles in solution as they really exist, a complete ionic equation can be written.
The sodium and nitrate ions are on both sides of the equation.
Such ions that do not participate in a reaction are called spectator ions.
An ionic equation that does not show spectator ions but only the particles that participate in a reaction is called a net ionic equation.
In the case of the reaction above, the net ionic equation from which the sodium and nitrate ions have been removed is as follows.

42. Writing Ionic Equations Example
10.3
Reactions in Aqueous Solutions
Writing Ionic Equations Example
Write the balanced chemical equation for the reaction between aqueous solutions of strontium nitrate and potassium sulfate, which forms the precipitate strontium sulfate.

43. Writing Ionic Equations Example
10.3
Reactions in Aqueous Solutions
Writing Ionic Equations Example
Write the complete ionic equation.
Cross out the spectator ions, which are those that are on both sides of the equation.
That leaves the net ionic equation.

44. 10.3
Reactions in Aqueous Solutions
Question 1
Write a balanced chemical, complete ionic, and net ionic equations for the following reaction:
Aqueous solutions of lead(II) nitrate and ammonium chloride are mixed, forming a precipitate of lead(II) chloride.

45. Be Prepared for Unit 7 Test.
End of Unit 7
Be Prepared for Unit 7 Test.