1. Chemical Reactions Ch 6

2. Essential questions part 1  What is a chemical reaction?  How can you tell a reaction has taken place?  What happens with energy in a chemical reaction?

3. Properties Physical property – a characteristic of a pure substance that can be observed without changing it into another substance. Chemical property – a characteristic of a pure substance that describes its ability to change into a different substance.

4. Changes Physical change – a change in a substance that does not change its identity. Chemical change – a change in which one or more substances combine or break apart to form new substances.

5. How does bonding create a chemical change?  chemical changes occur when bonds break and new bonds form.  Chemical reactions involve changes in properties and changes in energy that you can observe.

6. Chemical reactions cause: 1.Bonds to break 2.atoms to rearrange 3.New bonds to form

7. III. Evidence for chemical reactions The process where one or more substances change into one or more DIFFERENT substances.

8. clues that reactions occurred  A gas is formed – bubbling or fizzing  A solid is formed – precipitate (little chunks or cloudiness forms)  Color changes  Energy (temp.) changes  Odor changes  Any change that is a result of a new substance being formed

9. Changes in Energy  Endothermic – reaction that absorbs energy into the bonds from the environment, gets colder  Example: cooking  Exothermic – reaction that releases energy from the bonds to the environment – gets hotter  Ex: fire (fast), explosion (fast), rust (slow)

10. Energy in Chemical Reactions

11. Activation Energy: Energy used to start a reaction  Example:  friction used to start a match  Using a match to light a candle or bunsen burner

12. Compounds  Two or more elements that are chemically combined

13. Types of Compounds: Review 1.Covalent – formed from 2 or more nonmetals that share electrons 2.Ionic – formed from a metal and a nonmetal that transfer electrons to form charged ions 3.Metallic –formed when two metals share loose electrons between many positive metal ions

14. Describing Chemical Reactions Essential Questions 6.2  How do you describe a chemical reaction?  How is matter conserved during a reaction?

15. How to represent: Element – symbol Compound – formula Reaction – equation

16. Chemical Formula - short way to write the name of a compound 1.Tells – what kind of elements make up the compound (Look for symbols) 2.Tells – how many atoms of each element there are 3.Subscript – small number written below and after the symbol to tell how many atoms there are of that element. If there is no subscript, then there is 1 atom

17. Parts of an equation Reactants – a substance that undergoes change in a chemical reaction. Products – a substance formed as a result of a chemical reaction.

18. Formulas for covalent compounds When naming a covalent compound, a prefix is always used on the 2 nd element to indicate the number of atoms of the element in the compound. di – twotri – threemono – one Carbon dioxideCarbon monoxide Dihydrogen monoxide

19. D. Formulas for ionic compounds  The formulas must have a neutral charge (total charge of zero).  Positive and negative charges must be equal  Magnesuim fluorideMgF 2 Mg +2 2 F -1

20. Describing Chemical Reactions What are chemical equations?  Uses symbols and formulas to show what happens in a chemical reaction  Ex: NaOH + HCl NaCl + H 2 O

21. 2. Parts of an Equation a. Reactant (NaOH and HCl) b. Product (NaCl and H 2 O)

22. Traits of Chemical Reactions

23. 2. Parts of an Equation c. Arrow Means “produces” or “yields”. It tells you a reaction has taken place. d. Plus Sign Separates 2 or more elements or compounds in the reactant or product. e. Coefficient Number in front of the element or formula; it tells how many molecules there are.2HO

24. Chemical Equations

25. 6.3 Controlling chemical reactions Essential questions  What is the Law of Conservation of Matter/Mass?  How can you control the rate of a reaction?

26. V. Law of Conservation of Matter:  Matter or energy cannot be created or destroyed, - it only changes form  All atoms you started with in the equation are there at the end of the reaction, just REARRANGED

27. How to balance an equation:  CH 4 + O 2 CO 2 + H 2 O  1. List each element and the number of atoms  C = 1C = 1  H = 4H = 2  O = 2O = 3  2. Add a COEFFICIENT to balance the atoms on each side  CH 4 +2 O 2 CO 2 + 2 H 2 O  C = 1C = 1  H = 4H = 4  O = 4O = 4  3. RECHECK the number of atoms on each side of the equation.

28. VII. Rate of Chemical Reactions  How fast or slow a chemical reaction occurs depends on:  1. How hard the molecules bump into each other  2. How many times the molecules bump into each other

29. Things that affect reaction rate:

30. VIII. Rates of chemical reactions:  1. Surface area – higher surface area= faster reaction lower surface area = slower reaction  2. Temperature –higher temperature = faster reaction lower temp.= slower reaction

31. Things that affect reaction rates  3. Concentration – higher concentrations = faster reactions lower concent. = slower reaction  4. Catalyst: a substance that affects the rate of the reaction without being changed by the reaction Ex. Chlorophyll (speeds up reaction)  5. Inhibitors – a material that decreases the rate of a chemical reaction. (slows down reaction