1. Chemical Reactions

2. Chemical Reactions
Processes in which one or more substances are converted into new substances with different physical and chemical properties

3. Chemical Reactions
Processes in which one or more substances are converted into new substances with different physical and chemical properties
Ex: rusted metal, burned toast

4. Chemical Reactions Parts of a chemical reaction:
Reactants – substances before reaction occurs
Products – substances produced by the reaction

5. Chemical Reactions Reason why reactions occur:
Increase in stability for products

6. Types of Reactions
Combination - two substances combine to form new substance
A + B  AB
Ca + Cl2  CaCl2

7. Types of Reactions Combustion – substance reacts with oxygen
A + O2  AO
CH4 + O2  CO2 + H2O

8. Types of Reactions
Decomposition – substance breaks into two or more substances
AB  A + B
MnSO4  MnO + SO3

9. Types of Reactions
Single-replacement – uncombined element “trades places” with an element in a compound
A +BX  AX + B
Cd + 2 HCl  CdCl2 + H2

10. Types of Reactions
Double-replacement – two binary compounds “trade partners”
AX +BY  AY + BX
CaCO3 + 2 HCl 
CaCl2 + H2CO3

11. Chemical Equations
Sentences representing a chemical reaction

12. Chemical Equations 2 types
Word equations - gives names of reactants & products
Formula equations – shows chemical formulas and symbols

13. Chemical Equations Formula equations… Symbols used: + reacts/combines
with, and
 yields/produces
 precipitate formed
 gas emitted

14. Chemical Equations Formula equations… Symbols used: (s) solid state
(l) liquid state
(g) gaseous state
(aq) aqueous state

15. Chemical Equations Diatomic molecule reminder… Hydrogen H2 Nitrogen N2
Oxygen O2
Fluorine F2
Chlorine Cl2
Bromine Br2
Iodine I2

16. Chemical Equations Unbalanced Examples (aka Skeleton Equations):
Calcium reacts with oxygen to produce calcium oxide

17. Chemical Equations Unbalanced Examples (aka Skeleton Equations):
Carbon reacts with oxygen to produce carbon dioxide

18. Chemical Equations Unbalanced Examples (aka Skeleton Equations):
Solid sodium reacts with chlorine gas to produce solid sodium chloride

19. Chemical Equations Unbalanced Examples (aka Skeleton Equations):
Nitrogen gas reacts with hydrogen gas to produce ammonia gas

20. Chemical Equations Unbalanced Examples (aka Skeleton Equations):
Sodium hydroxide reacts with hydrogen chloride to produce water and sodium chloride

21. Chemical Equations Can include heat
Endothermic – heat, from surroundings, enters the system, has positive heat of reaction (DH) value, reactants have lower potential energy than products

22. Chemical Equations
Can include heat
Endothermic reaction

23. Chemical Equations Can include heat Endothermic reaction:
C(s) +2 S(s) kJ  CS2(l)
C(s) +2 S(s)  CS2(l)
DH = 89.3 kJ

24. Chemical Equations
Can include heat
Endothermic – heat, from surroundings, enters the system
Exothermic – heat exits the system and goes to surroundings, has negative heat of reaction (DH) value , reactants have higher potential energy than products

25. Chemical Equations
Can include heat
Exothermic reaction

26. Chemical Equations Can include heat Exothermic reaction:
CaO(s) + H2O(l)
 Ca(OH)2(s) kJ
CaO(s) + H2O(l)  Ca(OH)2(s)
DH = kJ

27. Chemical Equations Can include heat
For systems with a constant pressure, heat is also called enthalpy (so DH is also change in enthalpy)

28. Chemical Equations Can include heat
Enthalpy diagrams – visual representation of a thermochemical equation

29. Chemical Equations
Enthalpy diagrams – Endothermic reaction

30. Chemical Equations
Enthalpy diagrams – Exothermic reaction

31. Chemical Equations How to balance:
Write formula equation with correct formulas & symbols
Count number of atoms on each side of arrow (make table if needed)
Mass must be conserved (number of atoms on each side of arrow are equal), use coefficients to adjust
Work with one atom or ion at a time
Save H & O for last (they tend to be in more than one place & can be difficult)
Recount to ensure that number of atoms are equal on each side

32. Chemical Equations Balancing examples: NaOH + HCl  H2O + NaCl
Ca + O2  CaO

33. Chemical Equations Balancing examples: N2 + H2  NH3
CH4 + O2  CO2 + H2O

34. Chemical Equations Balancing examples: FeCl3 + Na2CO3
 NaCl + Fe2(CO3)3
C2H6 + O2  CO2 + H2O

35. Chemical Reactions Reaction Rates
Reactions happen if particles have enough energy.

36. Chemical Reactions Reaction Rates Factors Temperature Concentration
Surface area/Particle Size
Catalysts – substances that speed up reaction without being used

37. Chemical Reactions Reactions are reversible
When rate of forward and reverse reaction are equal, system is at equilibrium.

38. Chemical Reactions Reactions are reversible
Equilibrium is described by Le Chatelier’s principle
If stress is applied to a system, the system changes to relieve the stress

39. Chemical Reactions Reactions are reversible
Factors affecting equilibrium:
Concentration
Temperature
Pressure
Increasing pressure shifts equilibrium to whichever side has fewer particles. Decreasing pressure has opposite effect.

40. Chemical Reactions Reactions are reversible
Equilibrium is described by a constant
Keq, which is a ratio of products to reactants.
Keq > 1, products favored
Keq < 1, reactants favored