1. Chapter 24 – Chemical Reactions
Section 1 – Chemical Changes

2. Chapter 24 – Chemical Reactions
Section 1 – Chemical Changes
Describing chemical reactions – change of one or more substances converted into new substances

3. Chapter 24 – Chemical Reactions
Section 1 – Chemical Changes
Describing chemical reactions – change of one or more substances converted into new substances
Reactants are substances that combine or change

4. Chapter 24 – Chemical Reactions
Section 1 – Chemical Changes
Describing chemical reactions – change of one or more substances converted into new substances
Reactants are substances that combine or change
New substances that are produced are called products

5. + ->
Reactant + Reactant -> Product

6. Conservations of Mass – a law which states that, in a chemical reaction, matter is not created or destroyed; it stays the same

7. Conservations of Mass – a law which states that, in a chemical reaction, matter is not created or destroyed; it stays the same
Antoine Lavoisier – experimented with mercury (II) oxide and heat

8. Conservations of Mass – a law which states that, in a chemical reaction, matter is not created or destroyed; it stays the same
Antoine Lavoisier – experimented with mercury (II) oxide and heat
Found mass of products (liquid mercury and oxygen gas) equaled mass or reactants

10. Writing equations – a chemical equation uses chemical formulas and symbols to describe a chemical reaction and the products it produces

11. Writing equations – a chemical equation uses chemical formulas and symbols to describe a chemical reaction and the products it produces
Chemical formula expresses the relationship between elements in the compounds and molecules they make up

12. Writing equations – a chemical equation uses chemical formulas and symbols to describe a chemical reaction and the products it produces
Chemical formula expresses the relationship between elements in the compounds and molecules the make up
Coefficients – numbers which represent the number of units of each substance in a reaction

13. 2 H20
coefficient
= H2O + H2O

14. NiCl2 + 2NaOH Ni(OH)2 + 2NaCl

15. Knowing coefficients of chemical reactions allows chemists to use the correct amounts of reactants to predict the amounts of products

16. Knowing coefficients of chemical reactions allows chemists to use the correct amounts of reactants to predict the amounts of products
Subscripts – numbers which represent the number of atoms in a molecule of a particular element

17. H20
subscript
= H + H + O

18. Knowing coefficients of chemical reactions allows chemists to use the correct amounts of reactants to predict the amounts of products
Subscripts – numbers which represent the number of atoms in a molecule of a particular element
Symbols used to show state of reactants; (s) solid, (aq) aqueous [dissolved in water], (g) gas, (l) liquid

19. Metals react with atmosphere in different ways

20. Section 2 – Chemical Equations

21. Section 2 – Chemical Equations
Checking for balance – law of conservation of mass requirement

22. Section 2 – Chemical Equations
Checking for balance – law of conservation of mass requirement
A balanced chemical reaction – both sides of equation have same number of atoms of each element

23. Section 2 – Chemical Equations
Checking for balance – law of conservation of mass requirement
A balanced chemical reaction – both sides of equation have same number of atoms of each element
Choosing coefficients – becomes easier with practice; trial and error at first

24. 2Mg(s) + O2(g) -> 2MgO(s)
2 x Mg
2 x O
Fill in the missing coefficients:
_____ H2(g) + O2(g) -> _____ H2O (g)

25. 2Mg(s) + O2(g) -> 2MgO(s)
2 x Mg
2 x O
Fill in the missing coefficients:
__2__ H2(g) + O2(g) -> __2__ H2O (g)

26. Writing balanced chemical equations - a four-step process

27. Writing balanced chemical equations - a four-step process
Describe the reaction in words

28. When solid sodium is placed in water it forms aqueous sodium hydroxide and hydrogen gas.

29. Writing balanced chemical equations - a four-step process
Describe the reaction in words
Write the equation using formulas and symbols

30. When solid sodium is placed in water it forms aqueous sodium hydroxide and hydrogen gas.
Na(s) + H2O(l) -> NaOH(aq) + H2(g)

31. Writing balanced chemical equations - a four-step process
Describe the reaction in words
Write the equation using formulas and symbols
Check for balance

32. When solid sodium is placed in water it forms aqueous sodium hydroxide and hydrogen gas.
Na(s) + H2O(l) -> NaOH(aq) + H2(g)
1 x Na
1 x O
3 x H
2 x H

33. Writing balanced chemical equations - a four-step process
Describe the reaction in words
Write the equation using formulas and symbols
Check for balance
Add coefficients where needed for balance

34. Find the missing coefficients:
____ Na(s) + _____ H2O(l) ->
_____ NaOH(aq) + _____ H2(g)

35. Find the missing coefficients:
____ Na(s) + _____ H2O(l) ->
_____ NaOH(aq) + _____ H2(g)
_2__ Na(s) + __2__ H2O(l) ->
__2__ NaOH(aq) + __1__ H2(g)

36. _2__ Na(s) + __2__ H2O(l) -> __2__ NaOH(aq) + __1__ H2(g)
2 x Na
2 x O
4 x H
4 x H

37. Section 3 – Classifying Chemical Reactions

38. Section 3 – Classifying Chemical Reactions
Synthesis reaction – two or more substances form a new substance; A + B -> AB

39. Synthesis
Look for:
2 or more reactants, only one product

40. Section 3 – Classifying Chemical Reactions
Synthesis reaction – two or more substances form a new substance; A + B -> AB
One substance breaks down into two or more substances in a decomposition reaction; AB -> A + B

41. Decomposition
Look for:
only 1 reactant, 2 or more products

42. Section 3 – Classifying Chemical Reactions
Synthesis reaction – two or more substances form a new substance; A + B -> AB
One substance breaks down into two or more substances in a decomposition reaction; AB -> A + B
Single-displacement reaction - one element replaces another one in a compound; A + BC -> AC + B

43. Single Displacement Look for:
1 compound and ion forming another compound and ion

44. A double-displacement reaction results if a precipitate, water, or a gas forms when ionic compounds in solution are combined; AB + CD -> AD + CB

45. Double Displacement
Look for:
2 compounds forming 2 new compounds

46. Section 4 – Chemical Reactions and Energy

47. Section 4 – Chemical Reactions and Energy
Chemical reactions involve energy exchange

48. Section 4 – Chemical Reactions and Energy
Chemical reactions involve energy exchange
Breaking chemical bonds requires energy

49. Section 4 – Chemical Reactions and Energy
Chemical reactions involve energy exchange
Breaking chemical bonds requires energy
Forming chemical bonds releases energy

50. Section 4 – Chemical Reactions and Energy
Chemical reactions involve energy exchange
Breaking chemical bonds requires energy
Forming chemical bonds releases energy
More energy out

51. Exergonic reactions – energy required to break bonds is less than the energy released from new bonds; energy given off is usually light

52. Exergonic reactions – energy required to break bonds is less than the energy released from new bonds; energy given off is usually light
Exothermic reactions – energy given off in the form of heat

53. Exergonic reactions – energy required to break bonds is less than the energy released from new bonds; energy given off is usually light
Exothermic reactions – energy given off in the form of heat
More energy in

54. Endergonic reactions – more energy is required to break bonds than to form new ones

55. Endergonic reactions – more energy is required to break bonds than to form new ones
If energy needed is heat, the reaction is endothermic

56. Endergonic reactions – more energy is required to break bonds than to form new ones
If energy needed is heat, the reaction is endothermic
A catalyst speeds up a chemical reaction without itself being permanently changed

57. Endergonic reactions – more energy is required to break bonds than to form new ones
If energy needed is heat, the reaction is endothermic
A catalyst speeds up a chemical reaction without itself being permanently changed
An inhibitor prevents or slows a chemical reaction or interferes with a catalyst’s action