1. Chapter 21 Chemical Equations Section 1 Chemical Change

2. What is a chemical reaction?

3. A. Describing chemical reactions
Chemical Reactions- change of one or more substances converted into new substances
Reactants - substances that combine or change
Products- new substances that are produced
produce
Reactants  Products

4. B. Conservation of Mass
Conservation of Mass-a law which states that, in a chemical reaction, mass is not created or destroyed; it stays the same
Antione Lavoisier – Father of Modern Chemistry
Found mass of products equaled the mass of the reactants

5. C. Writing Equations
Chemical equation - uses chemical formulas and symbols to describe a chemical reaction and the products it produces
Chemical formula - expresses the relationship between elements in the compounds and molecules they make up
Symbols used to show physical state of reactants; (s) solids (aq) aqueous (g) gas (l) liquid

6. C. Writing Equations
Coefficients – whole numbers in front of the symbol, which represent the number of units of each substance in a reaction **Located before the symbols
Subscripts – small lowered numbers which represent the number of atoms in a molecule of a particular element
*Located after and below the symbols
Nomenclature – way to name things scientifically

7. Discussion Questions What does the law of conservation of mass state?
What is the function of coefficients in a chemical equation?

8. Answers
In a chemical reaction, matter is neither created nor destroyed. The total sum of the reactants must equal the sum of the product.
Chemist need to know how much of a reactant will produce a certain amount of product

9. Describe 3 chemical reactions that you have observed (EX: burning marshmallow)
There are many things that let you know it’s a chemical reaction: color change, forming a precipitate, production of heat.

10. Section 2 Chemical Equations

11. Checking for Balance
A balanced chemical reaction- both sides of equation have the same number of atoms of each element
Coefficients are used in front of the element or compound to balance.
Choosing coefficients - becomes easier with practice; trial and error at first

12. Writing balanced chemical equations - 4 step process
Describe the reaction in words
Write the equation using formulas and symbols
Check for balance
Add coefficients where needed for balance

13. Discussion Question
Why do chemical equations need to be balanced?

14. Answer
Law of conservation of mass says mass will not be created or destroyed

15. Section 3 Classifying Chemical Reactions

16. Types of Reactions
1. Synthesis Reaction- two or more substance form a new substance
A + B --> AB
2. Decomposition Reaction-One substance breaks down into two or more substances AB ---> A + B
3. Single-displacement Reaction- one element replaces another one in a compound; A + BC ---> AC +B or D + BC --> BD + C
4. Double-displacement Reaction- results if a precipitate, water, or a gas forms when two ionic compounds in a solution are combined; AB + CD --> AD + CB
5. Combustion Reaction-a substance combines with oxygen to produce energy
“X” + O2 --> CO2 + H2O

17. Oxidation-Reduction (Redox)
These reactions often involve oxygen
Oxidation
Loss of electrons
Substance becomes “oxidized”
Reduction
Gain of electrons
Substance becomes “reduced”

18. Discussion Questions
1. What two chemical reactions are “opposites” of each other and why?
2. What are the 5 types of chemical reactions?

19. Answers Synthesis and decomposition
synthesis multiple substances combine to form a new one
decomposition a single substance breaks apart into multiple simpler substances
Synthesis, decomposition, single-displacement, double-displacement, combustion

20. Section 4 Chemical Reactions and Energy

21. A. Chemical Reactions involve energy exchange
Exergonic-Breaking chemical bonds release energy
Endergonic-Forming chemical bonds requires energy
Exothermic-Chemical Reaction where energy is primarily given off in the form of heat
Endothermic-Chemical reaction that requires heat energy in order to proceed

22. B. More energy out
A catalyst speeds up a chemical reaction without itself being permanetly changed
An inhibitor prevents or slows a chemical reaction or interferes with the catalyst’s action

23. Discussion Question
How are chemical bonds involved in energy exchanges?

24. Answer
Breaking bonds release energy; forming bonds to require energy