1. Describing Chemical Reactions
Monterey Highlands School
Mr.Sapalicio
Physical Science & Chemistry

2. conservation of matter
Key Term
Definition
How I understand it
chemical equation
conservation of matter
coefficient
subscript
reactant
Product

3. Chemical Reactions?
Chemical equation- a short way to show chemical reactions using symbols/chemical formulas instead of words to summarize a reaction.
English- use a few letters to display reactions to make it a lot simpler.

4. Chemical Equations
Chemical equations use chemical formulas and other symbols instead of words to summarize a reaction
All chemical equations have a common structure
Equations tell you what substances you start with in a reaction and the substances (products) you get at the end.

5. ‘+’ signs are used to separate two or more reactants or products.
Chemical Equations
The number of reactants and products can vary
‘+’ signs are used to separate two or more reactants or products.

6. Parts of the Equation Symbol- Chemical formula- Subscript- Reactant-
Product-
Yields   gives you
Coefficient- The number placed in front of a chemical formula.

7. Label the Parts of the Equation

8. H2 O2 + 2H2O2 Parts of an Equation coefficient yields reactant
product
subscript

9. Conservation of Matter
During a chemical reaction matter is not created or destroyed
The total mass of the reactants must equal the total mass of the products
In a chemical reaction the number of atoms stays the same no matter how they are arranged

10. Open system Or Closed system
It is not always easy to measure all matter in a reaction because in some reactions matter enters or escapes to the surroundings
In an open system matter can enter or escape from the environment
In a closed system matter is not allowed to enter or leave

11. Parts of a Reaction Equation
Chemical equations show the conversion of reactants (the molecules shown on the left of the arrow) into products (the molecules shown on the right of the arrow).
A + sign separates molecules on the same side
The arrow is read as “yields”
Example
C + O2  CO2
This reads “carbon plus oxygen react to yield carbon dioxide”

12. The charcoal used in a grill is basically carbon
The charcoal used in a grill is basically carbon. The carbon reacts with oxygen to yield carbon dioxide. The chemical equation for this reaction, C + O2  CO2, contains the same information as the English sentence but has quantitative meaning as well.

13. Balancing Equations
When balancing a chemical reaction you may add coefficients in front of the compounds to balance the reaction, but you may not change the subscripts.
Changing the subscripts changes the compound. Subscripts are determined by the valence electrons (charges for ionic or sharing for covalent)

14. Subscripts vs. Coefficients
The subscripts tell you how many atoms of a particular element are in a compound. The coefficient tells you about the quantity, or number, of molecules of the compound.

15. Balancing Chemical Equations
Cu2O C Cu
CO2 + +
1. count the number of atoms of each element on each side of the equation Cu C Cu O C O

16. Cu2O C Cu CO2 + + 2. Put a box where coefficients can be placed. Cu C

17. 3. Add coefficients until all elements are cancelled out2
Cu2O C 4 Cu
CO2 + + Cu C Cu O C O Cu Cu O

19. Remember!
Balancing chemical equations is about using the Distributive Property and Multiplication!

20. Classifying Chemical Reactions
Synthesis- to put things together. When 2 or more reactants yield one product.
Reactant + Reactant  Product
Ex: H+O Water (2 1)
Decomposition- compounds break down into simpler products. One reactant yields 2 or more products.
Reactant Product + Product
Ex: 2H2O2 2H20 + O (1 2)

21. Classifying Chemical Reactions
Replacement- when one element replaces another in a compound, or when 2 elements in different compounds trade places.
What?- Imagine taking someone’s girlfriend or boyfriend. You have now replaced them.
Ex: 2Cu2O + C 4Cu + CO2
Reactant + Reactant  Product + Product

22. Learning Check R1 Classify the following reactions as
1) Synthesis or 2) decomposition:
___A. H2 + Br HBr
___B. Al2(CO3)3 Al2O3 + 3CO2
___C. 4 Al + 3C Al4C3

23. LecturePLUS Timberlake 99
Learning Check R3
Balance the combustion equation
___C5H ___O ___CO2 + ___H2O
LecturePLUS Timberlake 99

24. LecturePLUS Timberlake 99
Solution R3
Balance the combustion equation
1 C5H O CO H2O
LecturePLUS Timberlake 99

25. Practice
P. 229 Math Analyzing Data #1-2