1. Conservation of Mass Reaction Rate
review

2. Rate of Reaction
Collision Theory: Reactions occur as a result of successful collisions between atoms or molecules. If you can increase the number of successful collisions, then you can increase the rate of a reaction. CONVERSLY you can inhibit (slow down) a reaction if you reduce the number of successful collisions.

3. Increasing the rate
Temperature….how does it increase the number of successful collisions Surface area…how does it increase the number of successful collisions Concentration of reactants…how does it increase the number of successful collisions

4. Increasing the rate
Temperature….increasing temp increases the energy in molecules, so they move faster and have more collisions Surface area…a larger number of molecules are exposed so more molecules can collide sooner Concentration of reactants…this increases the number of molecules present, so “crowding” occurs and more collisions happen

5. Then there is a catalyst…
Catalysts are not chemically bonded to reactants or products. They act as “matchmakers,” by decreasing the amount of energy needed to complete the reaction and/or properly aligning the reactants.

6. Decreasing the rate
Temperature….how does it decrease the number of successful collisions Surface area…how does it decrease the number of successful collisions Concentration of reactants…how does it decrease the number of successful collisions

7. Decreasing the rate
Temperature….reducing the temperature decreases the amount of energy in the molecules, so they move slower and have fewer collisions Surface area…decreasing the surface area means fewer molecules are exposed to other molecules, as a result the number of molecules able to react is reduced and there are fewer collisions Concentration of reactants…diluting the concentration of reactants (reducing the concentration) means there are fewer molecules present in the same space, so they are more spread out and fewer collisions can occur.

8. Reactants and Products
Identify the reactants in the following reactions 2Na + 2H2O  2NaOH + ­­­H2 2Ag2O  4Ag + O2 S8 + 12O2  8SO3

9. Reactants and Products
Identify the reactants in the following reactions 2Na + 2H2O  2NaOH + 2H2 2 Ag2O  4Ag + O2 S8+ 12O2  8SO3

10. Reactants and Products
Identify the products in the following reactions 2Na + 2H2O  2NaOH + 2H2 2Ag2O  4Ag + O2 S8+ 12O2  8SO3

11. Reactants and Products
Identify the products in the following reactions 2Na + 2H2O  2NaOH + 2H2 2Ag2O  4Ag + O2 S8+ 12O2  8SO3

12. Law of conservation of mass
What is the law of conservation of mass? How does it relate to chemical reactions?

13. Law of conservation of mass
What is the law of conservation of mass?
Matter is not created or destroyed
Mass of reactants = mass of products
Total mass stays the same during a reaction
How does it relate to chemical equations?
Chemical equations must be balanced
Same elements present in reactants and products
Same number of each element in reactants and products.

14. Before balancing an equation, you need to know how to read a formula
2NaOH
8H2
4Ag
O2 
8H2SO4
What are the subscripts for each
of the following formulas?
What if an element doesn’t have
a subscript?
What information does the
subscript tell you?

15. Before balancing an equation, you need to know how to read a formula
2NaOH
8H2
4Ag
O2 
8H2SO4
What are the subscripts for each
of the following formulas?
What if an element doesn’t have
a subscript? We assume it’s a “1”
2H2O1
2Na1O1H1
What information does the
subscript tell you? The number of
atoms of each element in a
molecule.

16. Before balancing an equation, you need to know how to read a formula
2NaOH
8H2
4Ag
O2 
8H2SO4
What are the coefficients for each
of the following formulas?
What if a reactant doesn’t have
a coefficient?
What information does the
coefficient tell you?

17. Before balancing an equation, you need to know how to read a formula
2NaOH
8H2
4Ag
O2 
8H2SO4
What are the coefficients for each
of the following formulas?
What if a reactant doesn’t have
a coefficient? Then we assume it is
a “1”
e) 1O2 
What information does the
coefficient tell you? How many
molecules of a reactant are present
in a reaction

18. Rules for balancing a chemical equation
Change the coefficients (BIG NUMBERS),
do not change the subscripts (little numbers)
Why:?
If you change the subscript, you change the identity of the substance.
C6H12O6 is sugar
C4H6O2 is white glue
C3H8O is isopropyl alcohol

19. Steps to balance an equation
Draw a line down from the arrow
Write down the elements on each side of the equation
Count the number of atoms of each element on both sides of the equation
(distributive property: coefficient x subscript)
Change one coefficient at a time, redo your totals before changing another coefficient

20. Check to see if these are balanced if they aren’t balanced, balance them
P O  P2O5
CH O  CO H2O
NaCl F2  NaF Cl2

21. Check to see if these are balanced if they aren’t balanced, balance them
4P O  P2O5
CH O  CO H2O
2NaCl F2  NaF Cl2

22. Sometimes you are asked to demonstrate the law of conservation of mass this way…
40 g of Ca reacts with 71 g of Cl to produce _____ g of CaCl.
2. _____ g of potassium reacts with 16 g of oxygen to produce 94 g of potassium oxide.
3. 14 g of lithium react with _____ g sulfur to produce 46 g of lithium sulfide.
4. 24 g of magnesium reacts with 38 g of fluorine to produce _____ g magnesium fluoride.

23. Sometimes you are asked to demonstrate the law of conservation of mass this way…
1) g of Ca reacts with 71 g of Cl to produce 111 g of CaCl.
2) g of potassium reacts with 16 g of oxygen to produce 94 g of potassium oxide.
3) g of lithium reacts with 32 g sulfur to produce 46 g of lithium sulfide.
4) g of magnesium reacts with 38 g of fluorine to produce 62g magnesium fluoride.

24. Which of the following shows mass being conserved during a reaction?
2C8H O2  6CO2 + 18H2O b
2H2 + O2  2H2O c
2HgO  Hg + O2 d
2FeO2  Fe2 + O3

25. Which of the following shows mass being conserved during a reaction?
2C8H O2  6CO2 + 18H2O b
2H2 + O2  2H2O c
2HgO  Hg + O2 d
2FeO2  Fe2 + O3
Because it is balanced,
it shows that the mass during the reaction stayed the same

26. Every chemical reaction obeys the law of conservation of mass…
Every chemical reaction obeys the law of conservation of mass….but, sometimes a reaction makes it hard to observe.
What type of reaction circumstance would make it difficult to observe or measure the law of conservation of mass?

27. Every chemical reaction obeys the law of conservation of mass…
Every chemical reaction obeys the law of conservation of mass….but, sometimes a reaction makes it hard to observe.
What type of reaction circumstance would make it difficult to observe or measure the law of conservation of mass? An open system/container and gas as a reactant or product…..because if the system isn’t closed, the mass of the gas cannot be accounted for.

28. Review questions
What parts of an atom are involved in a chemical reaction? Why? What are the three types of physical changes? What is the difference between a physical and a chemical change?

29. Review questions
What parts of an atom are involved in a chemical reaction? Why? Electrons (valence electrons). Because matter behaves in a way to obtain stability..atoms become stable by completing their valence ring of electrons, they do this through bonding with other atoms. What are the three types of physical changes? Change in shape/size, dissolving, change in state/phase What is the difference between a physical and a chemical change? In a physical change, the substances do not change their identity..there are no bonds broken. In a chemical change, chemical bonds are broken and new bonds are created. New substances are formed in a chemical change by “rearranging” how atoms are bonded.

30. Review Questions
What information can you get from an atomic number? What happens during covalent bonding? What happens during ionic bonding?

31. Review Questions
What information can you get from an atomic number? The atomic number is the “ID number” of an element, it tells you what the element is. In a neutral atom, the atomic number tells you how many protons and how many electrons are in one atom of an element. In an ion, the atomic number only tells you the number of protons. What happens during covalent bonding? During covalent bonding, valence electrons are shared between 2 or more atoms. What happens during ionic bonding? During ionic bonding, valence electrons are transferred between atoms.