1. Endothermic and Exothermic Reactions
3_6: Chemical Energy
Endothermic and Exothermic Reactions

2. Al + HCl  AlCl3 + H2 K + Fe2(SO4)3  K2SO4 + Fe
Do Now
Balance the reactions below:
Al + HCl  AlCl3 + H2
K + Fe2(SO4)3  K2SO4 + Fe

3. 2Al + 6HCl  2AlCl3 + 3H2 6K + Fe2(SO4)3  3K2SO4 + 2Fe
Do Now
Balance the reactions below:
2Al + 6HCl  2AlCl3 + 3H2
6K + Fe2(SO4)3  3K2SO4 + 2Fe

4. Objective
I can determine whether a chemical reaction is endothermic or exothermic and draw an energy diagram for the reaction in a lab setting.

5. Agenda Do Now, Objective Vocabulary Mini-Labs Demo Lab
Introduction to Energy
Diagrams

6. Vocabulary
There are 2 types of chemical reactions. Those that ABSORB energy, and those that GENERATE energy.

7. Endothermic Reaction
Endothermic reactions ABSORB energy/heat from their surroundings.
When endothermic reactions occur, it makes the surroundings COLDER.
Students need to write down the definition for ‘endothermic reaction’

9. Exothermic Reaction
Exothermic reactions RELEASE energy/heat to their surroundings.
When exothermic reactions occur, it makes the surroundings HOTTER.
Students need to write down the definition for ‘endothermic reaction’

11. Mini-Labs
Working in groups of 3 you will observe an endothermic and an exothermic chemical reaction
Follow ALL directions
Write down your observations in the ‘lab’ section of your binder
Obey lab safety rules

12. Mini-Lab 1: Ammonium Nitrate & Water
Find the bag with small, white, pellets in it (10 g)
Add 20 mL of water to the bag and seal it
Observe what happens!
Pour the contents of your bag down the drain with the water running
Rinse out the plastic bag
Throw away the plastic bag
Write down your observations in the ‘lab’ section of your binder

13. Mini-Lab 2: Calcium Chloride OR Sodium Carbonate & Water
Find the bag with white crystals in it (20 g)
Add 20 mL of water to the bag and seal it
Observe what happens!
Pour the contents of your bag down the drain with the water running
Rinse out the plastic bag
Throw away the plastic bag
Write down your observations in the ‘lab’ section of your binder

14. Ammonium nitrate and water
NH4NO3 (s)   →   NH4+ (aq) + NO3-(aq)
Ammonium nitrate dissociates (dissolves) in water to form the ions ammonium and nitrate.
ENDOTHERMIC REACTION (absorbs heat)
This is the reaction that is used in ‘instant’ cold packs from first aid kits.

15. Calcium chloride and water
CaCl2 (s)   →   Ca2+ (aq) + Cl-(aq)
Calcium chloride dissociates (dissolves) in water to form the ions Ca2+ and Cl-.
EXOTHERMIC REACTION (releases heat)
This is the reaction that is used in ‘instant’ hot packs from first aid kits.

16. Ba(OH)2*8H2O(s) + 2NH4SCN(s)  Ba(SCN)2(aq) + 2NH3(g) + 10H2O(l)
Demo Lab
This reaction occurs between ammonium thiocyanate and barium hydroxide
Ba(OH)2*8H2O(s) + 2NH4SCN(s)  Ba(SCN)2(aq) + 2NH3(g) + 10H2O(l)
ENDOTHERMIC reaction
When the reaction occurs, heat is absorbed and the surroundings get colder, causing the ice to freeze

17. Day 2 – 96 minutes
Goals
Students can define endothermic, exothermic, activation energy, and change of enthalpy
Students can draw potential energy diagrams for endothermic and exothermic reactions

18. Do Now
What type of chemical reaction absorbs energy and requires energy for the reaction to occur?
What type of chemical reaction generates (makes) energy and requires energy for the reaction to occur?

19. Do Now
What type of chemical reaction absorbs energy and requires energy for the reaction to occur? ENDOTHERMIC REACTION
What type of chemical reaction generates (makes) energy and requires energy for the reaction to occur? EXOTHERMIC REACTION

20. Al + HCl  AlCl3 + H2 K + Fe2(SO4)3  K2SO4 + Fe
Do Now
Balance the reactions below:
Al + HCl  AlCl3 + H2
K + Fe2(SO4)3  K2SO4 + Fe

21. 2Al + 6HCl  2AlCl3 + 3H2 6K + Fe2(SO4)3  3K2SO4 + 2Fe
Do Now
Balance the reactions below:
2Al + 6HCl  2AlCl3 + 3H2
6K + Fe2(SO4)3  3K2SO4 + 2Fe

22. Objective
I can determine whether a chemical reaction is endothermic or exothermic by analyzing potential energy diagrams.

23. Agenda Do Now, Objective Vocabulary Review Potential Energy Diagrams
Guided Reading
Chem Review Questions
Weekly Quiz

24. Endothermic Reaction
Endothermic reactions ABSORB energy/heat from their surroundings.
When endothermic reactions occur, it makes the surroundings COLDER.
Students need to write down the definition for ‘endothermic reaction’

25. Examples of Endothermic Reactions
Cooking an egg
Melting ice
Splitting a gas molecule apart
Photosynthesis
sunlight + 6CO2 + H2O = C6H12O6 + 6O2

26. Exothermic Reaction
Exothermic reactions RELEASE energy/heat to their surroundings.
When exothermic reactions occur, it makes the surroundings HOTTER.
Students need to write down the definition for ‘endothermic reaction’

27. Exothermic Chemical Reaction Examples
Combustion of fireworks
Burning of natural gas
2H2 + O2 → 2H2O + heat

28. Guided Practice Which change is exothermic? freezing of water
melting of iron
vaporization of ethanol
sublimation of iodine
Why?
Heat is released as molecules slow down going from a liquid to a solid

29. Guided Practice Which of the following changes is endothermic?
freezing of water
A candle flame
Dissolving ammonium nitrate
Baking bread
Why?
The bread dough must absorb energy before it will bake.

30. Vocabulary
Activation Energy (Ea): The minimum energy required to start a chemical reaction
Change in Enthalpy (ΔH): The change in energy in a system that undergoes (has) a chemical reaction). Also called the ‘heat of reaction’. Measure in kJ.
+ΔH = the reaction absorbs energy  endothermic
-ΔH = the reaction releases energy (fire!)  exothermic

31. Endothermic Reaction Potential Energy (kJ)
Transition state
Potential Energy (kJ)
+ΔH = endothermic reaction
Heat is absorbed during the reaction, this is why there is MORE potential energy at the end of the reaction, than at the beginning

32. Exothermic Reaction Potential Energy (kJ)
Transition state
reactants
Potential Energy (kJ)
This is a potential energy diagram
P.E. stands for potential energy
-ΔH = exothermic reaction
products
Heat is released from the reaction, this is why there is LESS potential energy at the end of the reaction, than at the beginning

33. Guided Practice
Which of the following potential energy diagrams represent:
A endothermic reaction?  
An exothermic reaction?

34. Guided Practice
Which of the following potential energy diagrams represent:
A endothermic reaction?  C
An exothermic reaction? A

35. Guided Practice
Which statement correctly describes an endothermic chemical reaction?
The products have higher potential energy than the reactants, and the H is negative.
The products have higher potential energy than the reactants, and the H is positive.
The products have lower potential energy than the reactants, and the H is negative.
The products have lower potential energy than the reactants, and the H is positive.

36. Guided Practice Given the balanced equation:
Which phrase best describes this reaction?
endothermic with H = kJ
endothermic with H = kJ
exothermic with H = kJ
exothermic with H= kJ

37. S(s) + O2 (g)  SO2 (g) + energy
Guided Practice
Given the following reaction:
S(s) + O2 (g)  SO2 (g) + energy
Is the reaction endothermic or exothermic?
Exothermic

38. Guided Reading
Complete the guided reading with a partner making sure to answer ALL questions
a whisper

39. Chem Review Questions – Writing
Identify the following changes as endothermic or exothermic. (Hint: ask yourself whether the reaction requires the addition of heat energy to occur or does it release energy in the form of heat).
Melting ice
Lighting a match
Dry ice subliming into carbon dioxide gas
Frying an egg
Burning gasoline
Explosion of hydrogen gas when it reacts with oxygen gas

40. Chem Review Questions Melting ice – endothermic
Lighting a match – endothermic, the reaction requires the addition of energy to raise the energy level of the reactants to the point where the reaction begins, and can continue without further energy input
Dry ice subliming into carbon dioxide gas – endothermic, it has to absorb energy to warm up
Frying an egg – endothermic, energy must be supplied to the egg in order to start the reactions and cook it until adequately fried
Burning gasoline – exothermic, energy is released and powers the car
Explosion of hydrogen gas when it reacts with oxygen gas - exothermic

41. Weekly Quiz
Silently complete your quiz. When you are finished, turn it in and quietly put away your materials.
GOOD LUCK!

42. C6H4Cl2(solid) + energy  C6H4Cl2(gas)
Which process is exothermic
Boiling of water
Melting of copper
Vaporization of CO2
Freezing of ice
Given the balanced equation representing a phase change:
C6H4Cl2(solid) + energy  C6H4Cl2(gas)
It is endothermic and heat is released
It is exothermic and heat is released
It is endothermic and heat is absorbed
It is exothermic and heat is absorbed

43. Compare and contrast endothermic and exothermic reactions
Compare and contrast endothermic and exothermic reactions. Make sure your answer includes the word energy.
2H2O2  2H2O + O2. Identify the type of chemical reaction represented by the balanced reaction (synth, decomp, single replacement, etc.)

44. Balance
Zn + HCl  H2 + ZnCl2
Which equation represents a decomposition reaction?
CaCO3  CaO + CO2
Cu + 2AgNO3  2Ag + Cu(NO3)2
2H2 + O2  2H2O
KOH + HCl  KCl + H2O