Forming new substances

1. Ch 6 – Chemical Reactions Forming new substances

2. Matter and Change Changes in matter can be described in terms of physical changes and chemical changes Physical property – characteristic of a substance that can be observed w/out changing the substance into another substance • Color, hardness, texture, shine, flexibility, conducting heat and electricity Chemical property – characteristic of a substance that describes its ability to change into another substance • Flammability, rust, reativity

3. Physical change – any change that alters the form or appearance of a substance (can get back what you started with) Chemical change – change in matter that produces one or more new substances Chemical changes occur when bonds break and new bonds form

4. Chemical Reactions Involve changes in properties and changes in energy that you can observe.

5. Evidence to a Chemical Rxn • Gas formation • Solid formation – called a precipitate • Color change • Energy change (heat)

6. Chemical Formulas Shorthand way of using chemical symbols and numbers to represent a compound or group of elements. Shows the number of atoms of each element present in the formula.

7. i.e. - chemical formula for water = H2O tells us that it is composed of 2 hydrogen atoms and 1 oxygen atom Ex. O2 C6H12O6 Na2SO4

8. The small numbers are referred to as subscripts Common Prefixes: Mono = 1 Di = 2 Tri = 3 Tetra=4 Penta = 5 Hexa= 6 Hepta = 7 Octa = 8 Nona = 9 Deca = 10

9. Writing Formulas Covalent compounds made of 2 nonmetals CO2 = Carbon “di” oxide N2O = Dinitrogen monoxide N3O5 = ??

10. Ionic compounds made with a metal and a non-metal The compounds overall charge = zero NaCl = Sodium chloride (Na is a +ion and Cl is a –ion) MgCl2 = Magnesium chloride (Mg is a 2+ion, so we need 2 –ions of Cl)

11. Chemical Equation Description of a chemical rxn using chemical formulas and symbols i.e. H2 + O2→H2O Hydrogen + Oxygen YieldsWater

12. Equation Terms Reactants starting materials & ALWAYS on left Products formed materials & ALWAYS on right Coefficient a number placed in front of a chemical symbol or formula ( a regular size number )

13. Carbon + Oxygen Yields Carbon dioxide C + O2 → CO2 REACTANTSPRODUCTS Example of Coefficient: 3CO2- the “3” is the coefficient

14. Law of Conservation of Matter Matter is neither created nor destroyed in ordinary chemical/physical changes

15. Balancing Chemical Equations A chemical equation must show the same number of each type of atom on both sides of the equation. Steps to Balance an Equation • Write the equation • Count the atoms • Use coefficients to balance atoms • Look back and check

16. 1. Write the equation H2 + O2→ H2O • Count the atoms ReactantsProducts H = 2, O = 2 H = 2, O = 1 • Use Coefficients to balance atoms change H2O to 2H2O makes products H=4, O=2 H2 + O2 → 2H2O then change H2 to 2H2 makes reactants H=4,O=2 2H2 + O2 → 2H2O • Look Back and Check Reactants: H=4, O=2 Products: H=4, O=2 Balanced Equation 

17. 4 Types of Chemical Rxns • Synthesis • Decomposition • Single Replacement • Double Replacement

18. 1. Synthesis Rxn Two or more substances combine to form a single compound. *To Put together* 2Na + Cl2→ 2NaCl

19. → +

20. 2. Decomposition *To Take Apart* A single compound breaks down to form two or more simpler substances. H2CO3→ H2O + CO2

21. → +

22. 3. Single Replacement Rxn An element takes the place of another element that is part of a compound. Zn + 2HCl → ZnCl2 + H2

23. + → +

24. 4. Double Replacement Rxn Ions in two compounds switch places. NaCl + AgNO3→ NaNO3 + AgCl

25. → + +

26. Diatomic Molecules There are 7 molecules that always appear as diatomic (with 2 atoms) Br2 Cl2 F2 H2 I2 O2 N2

27. Law of Conservation of Energy Energy can neither be created nor destroyed Every rxn involves energy

28. Energy & Reactions There is a “certain” amount of energy required to make substances react. This is called the - Activation Energy

29. Exothermic Rxn A rxn in which energy is “released” or “removed”. (Exit = to leave, etc) Energy can be released as: Light, Heat, or Electrical energy 2Na + Cl2→ 2NaCl + energy

30. Endothermic Rxn A chemical rxn in which energy is “absorbed” or enters the rxn. (Enter = to come in) 2H2O + energy→ 2H2 + O2

31. Factors that affect Rates of Rxn 1. Temperature • Increase temp = increase rxn • Decrease temp = decrease rxn 2. Concentration [ ] Inc [ ] = Inc rxn 3. Surface area Inc SA = Inc rxn

32. 4. Catalyst Substance that speeds up a rxn Lowers the Activation Energy Biological catalyst is called an enzyme • Inhibitor slows down or stops rxn (i.e. preservatives and poison)