Mr. smith's science class ndcl 2014

1. Chemical Reactions
CHAPTER 7
Physical Science
Textbook: Physical Science Concepts in Action
Prentice Hall © 2009
© J. O’Reilly 2012

2. Describing Reactions
© J. O’Reilly
Chapter 7.1

3. 7.1 Describing Reactions
Objectives
By the end of
this section of
the book, you
should be able
to…
You might want to
leave space in your
notes between
objectives so you can
answer them later!
© J. O’Reilly
• Understand the law of conservation
of mass
• Balancing chemical reactions
• Compare atomic level structure to
visible structure for ionic
compounds

4. Key Terms
 – I know exactly
what the word
means and I
could teach it to
someone else.
 – I know the
word and could
probably use it
correctly.
 – Huh?
7.1 Describing Reactions
© J. O’Reilly
_____ product _____
_____ reactant _____
_____ law of conservation of mass_____

5. Chemical Equations
• Describe change by including what is present
before & after that change
– Reactants – undergo change
• Before change
– Products – formed from the change
• After change
• Reactants change into products
REACTANTS  PRODUCTS
© J. O’Reilly

6. Chemical Equations
• Reactants & products are expressed as formulas
– C + O2
 CO2
– How many atoms of each element are on each side of
the equation
– 1 C and 2 O on the reactant side
– 1 C and 2 O on the product side
– It’s a balanced equation! Just like in Math.
© J. O’Reilly

7. Conservation of Mass & Balancing
Equations
• Mass is never created nor destroyed in a chemical
reaction (rxn)
• Aka law of conservation of matter
H2 + O2
 H20
Do the number of atoms of each elements on each side
add up?
© J. O’Reilly

8. Balancing Equations
• Mass is conserved during a rxn  chemical
equation must be balanced
– Balance by changing coefficients
• Numbers that appear before the formula
• No coefficient listed ~ assumed 1
H2 + O2
 H20
H2 + O2
 2H2O
2H2 + O2
 2H2O
© J. O’Reilly

9. Try another one
• Ca + NaCl ----> Na + CaCl2
• 1- Count # of atoms for each element on both sides
• 2- Find one element that is imbalanced
• 3- Add a coefficient to balance both sides
• 4- Recount and add more coefficients to fix anything your
coefficent changed
– Try and balance 1 element at a time, and don’t worry if
you have to bounce back and forth a few times as you add
coefficients, that is normal.
– You CANNOT change subscripts (little numbers) as that
would change the chemical formula, only add coefficients
before the molecule
© J. O’Reilly

10. Types of Reactions
© J. O’Reilly
Chapter 7.2

11. Energy Changes in Reactions
© J. O’Reilly
Chapter 7.3