Chemical Reactions

1. Chemical Reactions

2. Chemical Reaction-Definition • A chemical reaction is a process in which the physical and chemical properties of the original substances change as new substances with different physical and chemical properties are formed

3. A sparkler contains magnesium. This, when lit, reacts with oxygen in the air and produces light and heat.  The chemicals inside a rocket, when lit, react with the oxygen in the air and produce heat, light and sound Examples of Chemical Reactions

4. Characteristics of Chemical Reactions • All chemical reactions result in the formation of a new substance • REACTANT: A substance involved in a chemical reaction • PRODUCT: The substance that is produced by a chemical reaction

5. Example of a Chemical Reaction + AIR = Product Reactant

6. Bonding Capacity • Bonding capacity is the ease at which an atom will form chemical bonds and it will determine its ability to undergo chemical reactions • Atoms with full outermost shells will not bond • Atoms with an incomplete outermost energy level will bond readily

7. Chemical Equations • Chemical equations describe a chemical reaction • Mg + O2 MgO + Energy • Magnesium + Oxygen Magnesium oxide + energy

8. Conservation of Mass • Atoms cannot be created or destroyed during a chemical reaction • The number of atoms of each element must be the same before and after the chemical reaction

9. Conservation of Mass • The changes that occur during any chemical reaction involve only the rearrangement of atoms, not their production or destruction

10. Conservation of Mass • All atoms have a mass • The total mass of the reactants MUST equal the total mass of the products • This is known as the Conservation of Mass

11. Balancing Chemical Equations • Mg + O2 MgO + Energy • This is not balanced • What do we do? • 2Mg + O2 2MgO + energy

12. Rules to Remember • Write the equation for the reaction making sure the symbols and formulas for the reactant and the products are correct. BaCl2 + H2SO4 BaSO4 + HCl

13. Rules to Remember • Count the number of atoms of each element on each side of the arrow. If the numbers are the same the equation is balanced BaCl2 + H2SO4 BaSO4 + HCl 1 Ba 2 H 1 Ba 1 H 2 Cl 1 S 1 S 1 Cl 4 O 4 O

14. Rules to Remember • If the number of atoms are not the same you need to use coefficients to balance the equation. BaCl2 + H2SO4 BaSO4 + 2HCl

15. Rules to Remember • Check your work by counting the atoms of each element to make sure they are the same BaCl2 + H2SO4 BaSO4 + 2HCl 1 Ba 2 H 1 Ba 2 H 2 Cl 1 S 1 S 2 Cl 4 O 4 O

16. Types of Chemical Reactions • There are four type of general reactions • Synthesis • Decomposition • Single replacement • Double replacement

17. Synthesis Reaction • Two or more simple substance combine to form a new more complex substance. • A + B C • 2Na + Cl2 2NaCl • The corrosion of metal is a synthesis reaction

18. Fun way to remember Synthesis Reactions In the cartoon, the skinny bird (reactant) and the worm (reactant) combine to make one product, a fat bird.

19. Example of Synthesis Reaction

20. Synthesis Reaction

21. Decomposition Reaction • A complex substance breaks down into two or more simpler substances. • C A + B • H2CO3 H2O + CO2

22. Fun Way to Remember Decomposition Reactions In this cartoon the egg (the reactant), which contained the turtle at one time, now has opened and the turtle (product) and egg shell (product) are now two separate substances.

23. Decomposition Reaction http://www.cnn.com/US/9604/23/newsbriefs/newimplo.mov

24. Single Replacement Reaction • An uncombined element replaces an element that is part of a compound • A + BX Ax + B • 2Na + 2H2O 2NaOH + H2

25. Fun Way to Remember Single-Replacement reactions Notice, the guy in the orange shirt steals the date of the other guy. So, a part of one of the reactants trades places and is in a different place among the products.

26. Double Replacement Reactions • Different atoms in two different compounds replace each other • AX + BY AY + BX • MgCO3 + 2HCL MgCl3 + H3CO3

27. A Fun Way To Thing of Double-Replacement Reactions The two old men swap hats in a double-replacement reaction

28. Double Replacement Reaction Pb(NO3)2 + 2KI --> 2KNO3 + PbI2 Potassium iodide reacts with lead nitrate to yield lead iodide and potassium nitrate.

29. Characteristics of Chemical Reactions • All chemical reactions involve a change in energy • Energy is either absorbed or released

30. Video of Energy Being Released http://www.usoe.k12.ut.us/curr/science/sciber00/8th/matter/movies/can.mov http://www.miramar.sdccd.cc.ca.us/faculty/fgarces/zCourse/Spring05/Ch100_OL/aMy_FilesLab/06Lb_Expt/Ex06_StudyChemRxn/06_RxnEthanol.mov

31. Exothermic Reactions • Chemical reactions in which energy is released • Heat comes out of the reaction • Energy of product is less than the energy of the reactant

32. Exothermic reactions http://cwx.prenhall.com/petrucci/medialib/media_portfolio/text_images/019_THERMITE.MOV

33. Endothermic Reactions • A chemical reaction in which energy is absorbed • Usually in the form of heat or light • Energy of the product is more than the energy of the reactant

34. Activation Energy • In order for reactants to form products the molecules combine to form a short-lived, high energy, unstable molecule. • This molecule then rearranges to form the product • This process requires energy called activation energy

35. Rate of Chemical Reactions • Kinetics is the study of reaction rates • Reaction rates are how quickly reactants turn into products

36. Collision Theory • Chemical reactions occur when bonds between atoms are broken and rearranged • In order for this to happen particles must collide • Collisions must occur at the right angle and with the right amount of energy

37. Collision Theory Cont. • The more collisions that occur the faster the rat of the chemical reaction.

38. Collision Theory Cont. • According to the collision theory: The rate of a reaction is affected by four factors: concentration, surface area, temperature and catalysts.

39. Concentration • Concentration is the amount of a substance. • High concentration of reactants means are many particles available for collision • More collisions occur so more products are formed

40. Concentration • A lower concentration means fewer collisions so a slower reaction rate • Example: when you light a fire it will burn, but it burns quicker when you blow on it because you are increasing the concentration of oxygen

41. Surface Area • Surface area refers to how much of a material is exposed • An increase in surface area increases the collisions between the reactants. • Example: 1 pound of sawdust will burn faster than a 1 pound log

42. Temperature • Temperature measures the energy of motion • Particles at a higher temperature move faster • Particles at high temperature collide more often • Particles at high temperature collide with more energy • Increate temperature increase reaction rate

43. Catalysts • Catalysts is a substance that increases the rate of a reaction but does not change itself. • Example: it would take weeks to digest a chocolate chip cookie, but substances in our stomach speed up the process

44. Catalysts • A catalysts decreases the activation energy needed for the reaction to occur. • Not as much energy is required so more collisions occur • Use catalysts in the early steps of the reaction

45. Catalysts • Cars have a catalytic converter which speeds up the reaction rate that changes the harmful gases into harmless ones. • Catalysts in our body are called enzymes which increase the rate of specific reactions involved in our bodies metabolism