2. Chapter Seventeen: Chemical Change
17.1 Chemical Reactions
17.2 Balancing Equations
17.3 Classifying Reactions

3. 17.1 Chemical Reactions
A chemical reaction is the process of breaking of chemical bonds in one or more substances, and the reforming of new bonds to create new substances.
When you make pizza, which changes are physical and which are chemical changes?

4. 17.1 Evidence of chemical change
Four indicators of chemical change are:
Formation of new gas
Formation of new solid
Release of energy (heat or light)
Color change

5. 17.1 Products and reactants
In chemical reactions, you start with reactants that are combined to make products.
The reactants are the starting substances.
The products are the new substances which result from the chemical reaction.

7. 17.1 Reactants and products
In the reaction, methane (a natural gas) is burned or combusted.
Some energy is added to get the reaction started.

8. 17.2 Balancing Equations
Antoine Laurent Lavoisier, established an important principal based on his experiments with chemical reactions.
He stated that the total mass of the products of a reaction is equal to the total mass of the reactants.
The law of conservation of mass holds true for even a burning mass of wood.

9. 17.2 Balancing Equations
The combined mass of the burning wood and oxygen is converted into carbon dioxide and water.

10. 17.2 Conservation of mass
Lavoisier showed that a closed system must be used when studying chemical reactions.
When chemicals are reacted in a closed container, you can show that the mass before and after the reaction is the same.

11. 17.2 Formula mass
The sum of the atomic mass values of the atoms in a chemical formula is called the formula mass.

12. 17.2 Avogadro’s Number
The Avogadro number was named in honor of Amedeo Avogadro who discovered that a mole of any gas under the same conditions has the same number of molecules.
Johann Josef Loschmidt, a German physicist, named and discovered the Avogadro number.
Loschmidt realized that a mole of any substance—be it a gas, liquid, or solid— contains 6.02 x 1023 atoms or molecules.

13. 17.2 Molar Mass
The mass (in grams) of one mole of a compound is called its molar mass.

14. What is the molar mass of one mole of CaCO3? Looking for: Given
Solving Problems
What is the molar mass of one mole of CaCO3?
Looking for:
… molar mass of CaCO3
Given
… chemical formula
Relationships:
no. amu in formula = molar mass in grams

15. Formula mass CaC03 = 100.19 g 1 mole CaC03 = 100.19 g CaCO3
Solving Problems
Solution
Formula mass CaC03 = g
1 mole CaC03 = g CaCO3

16. 17.2 Chemical Equations
When a chemical reaction is written using chemical formulas and symbols, it is called a chemical equation.

17. 17.2 Chemical equations
An arrow is always included between reactants and products.
It means “to produce” or “to yield.”
to produce
Reactants
Products
“Methane combines with oxygen gas to produce carbon dioxide gas and water vapor.”

18. 17.2 Numbers in equations

19. 17.2 Balancing equations
The law conservation of mass is applied by balancing the number and type of atoms on either side of the equation.

20. 17.2 Balancing equations
Counting atoms is necessary to balance an equation.
How many carbon atoms?
How many hydrogen atoms?
How many oxygen atoms?

21. 17.2 Steps for balancing
If not provided, write the word form of the equation.
Calcium carbonate reacts with hydrochloric acid to produce calcium chloride, carbon dioxide and water.

22. 17.2 Steps for balancing
If not provided, write the chemical equation from the word form.

23. 17.2 Steps for balancing
Count the number of each type of atom on both sides.

24. 17.2 Steps for balancing
Add coefficients to balance the equation.

25. Solving Problems
In this reaction, chalcocite (a mineral) reacts with oxygen in the presence of heat. The products are a type of copper oxide and sulfur dioxide. Balance this equation:
Cu2S + O2 → Cu2O + SO2

26. Looking for: Given Solving Problems
…the coefficients for each molecule
Given
… chemical formulas which show types and no. of atoms

27. Relationships Solving Problems
Coefficients can be added in front of any chemical formula in a chemical equation.
When a coefficient is added in front of a chemical formula, all atoms in that formula are multiplied by that number.
Use common denominators to help choose coefficients to try.

28. Solution- Trial and error
Solving Problems
Solution- Trial and error

29. 17.3 Addition reactions
The process of creating large molecules from small ones is called polymerization.

30. 17.3 Addition reactions
In an addition reaction, two or more substances combine to form a new compound.

31. 17.3 Decomposition reactions
A chemical reaction in which a single compound is broken down to produce two or more smaller compounds is called a decomposition reaction.

32. 17.3 Single Displacement
In a single-displacement reaction, one element replaces a similar element in a compound.

33. 17.3 Double Displacement
In a double-displacement reaction, ions from two compounds in solution exchange places to produce two new compounds.
One of the compounds formed is usually a precipitate that settles out of the solution, a gas that bubbles out of the solution, or a molecular compound such as water.

34. 17.3 Precipitation reactions
A precipitate is a new solid product that comes out of solution in a chemical reaction.
The formation of a cloudy precipitate is evidence that a double-displacement reaction has occurred.

35. 17.3 Precipitation
The limewater test for carbon dioxide is a precipitation reaction.

36. 17.3 Combustion reactions
A combustion reaction, also called burning, occurs when a substance such as wood, natural gas, or propane combines with oxygen and releases a large amount of energy in the form of light and heat.

37. 17.3 Combustion reactions
What do reactants like wood, natural gas, and propane have in common?