1. Chemistry Cornerstone 3
Sub-zero
Chemistry Cornerstone 3

2. Why do some athletes need cold packs? How do hand warmers work?
Warm-up
Why do some athletes need cold packs?
How do hand warmers work?
What do the prefixes endo and exo mean?

3. OBJECTIVES
By the end of the Cornerstone, SWBAT
Explain basic principles of Calorimetry.
Calculate energy released/absorbed by endothermic and exothermic reactions.
Carry out an experiment to collect data on endothermic and exothermic reactions.
Explain Endothermic and Exothermic Reactions.
Create a hand warmer based on data collected from experiments.

4. Endothermic vs. Exothermic Reactions
Endothermic reaction = Is a reaction that takes in energy (heat) from the surroundings.
reactants + energy → products

5. Endothermic Reactions

6. Endothermic Reactions
Examples of Endothermic Reactions:
1. Evaporation of water
2. Melting of ice
3. Photosynthesis

7. Endothermic vs. Exothermic Reactions
Exothermic reaction = A chemical reaction that releases energy in the form of heat.
reactants → products + energy

8. Exothermic Reactions

9. Exothermic Reactions Examples of Exothermic Reactions:
Combustion reactions
Cellular respiration
Freezing water

10. Basics of Heat and Energy
Chemical reactions can either release energy (“exothermic”) or absorb energy (“endothermic”).

11. Endothermic vs. Exothermic
Heat going in
Heat being used up
Feels cold!
Heat going out
Heat being made
Feels hot!

12. Signal Cards
Read the following questions, and hold up a green card for endothermic reactions and a red one for exothermic ones.
Everyone at the same time- wait until I say, “1, 2, 3 UP!” to put up your answer.
Use your notes to help you!

13. Checking for Understanding
Endothermic or Exothermic?
Ice melting
Burning a piece of wood
Pour a substance into a glass of water, then it gets cold
Mixing two substances in a cup, then it gets warmer
Water evaporating from grass

14. Chemical Bonds- formation and breaking
Chemical reactions are all around and within us.
Examples: Respiration, photosynthesis, manufacturing of new products and cooking.
During chemical reactions chemical bonds are broken and also formed.
The breaking of bonds absorbs energy.
The formation of bonds releases energy.
Enthalpy (∆H) is the energy changes in a chemical reaction.
If the process requires the input of energy the change of enthalpy (∆H) is positive.
If the process releases energy the change in enthalpy is negative.

15. Thermochemistry
Thermochemistry is the study of the energy changes that occur during chemical reactions and phase changes.

16. Basics of Heat and Energy
Energy is defined as the capacity to do work or to transfer heat.
The SI unit of energy is the joule, abbreviated with J.
Another common unit of energy is the calorie which is equal to J.
A calorie is defined as the amount of energy needed to raise the temperature of 1 g of water by 1ºC.

17. Example and Practice #1. 1 calorie = 4.184 J
A reaction produces 120 J of heat. Determine the number of calories.
Practice #1: a chemical reaction produces 1,200 calories. Determine the number of Joules.

18. Basics of Heat and Energy
Heat, represented by q, is the amount of energy transfers between objects with different temperatures.
Heat always flows from hot to cold.

19. Measuring Heat Flow
A calorimeter is used to measure the absorption or release of heat in a chemical or physical change.

20. Measuring Heat Flow
The amount of heat needed to raise the temperature of 1 gram of substance by 1ºC is called the specific heat capacity.
Metals have low specific heat values, meaning that they get hot very quickly.
 Substance  S
(J/g 0C)
 C (J/0C) for 100 g
Air
1.01
101
Aluminum
0.902
90.2
Copper
0.385
38.5
Gold
0.129
12.9
Iron
0.450
45.0
Mercury
0.140
14.0
NaCl
0.864
84.4
Ice
2.03
203
Water
4.179
417.9

21. Measuring Heat Flow
By contrast, liquid water has a high specific heat capacity and, therefore, requires more energy to raise its temperature.
 Substance  S
(J/g 0C)
 C (J/0C) for 100 g
Air
1.01
101
Aluminum
0.902
90.2
Copper
0.385
38.5
Gold
0.129
12.9
Iron
0.450
45.0
Mercury
0.140
14.0
NaCl
0.864
84.4
Ice
2.03
203
Water
4.179
417.9

22. Measuring Heat Flow q = m c T q = heat, m = mass c = specific heat
T = change in temp
C is a constant specific to an individual substance
You can determine if a reaction is endothermic or exothermic based on the sign of ∆H: negative means exothermic and a positive sign means that the reaction is endothermic.

23. Example #2
How many joules of heat are needed to raise the temperature of a 250 gram piece of aluminum from 25ºC to 125ºC?

24. Practice #2
How many joules of heat are needed to completely evaporate 250 grams of water? The heat of vaporization of water is 40.7 kJ/mol.
In a closed system, the heat lost by one object equals the heat gained by another. The quantitative study of heat flow in a closed system is called Calorimetry.

25. Signal Cards
Read the following questions, and hold up an A, B, C based on your answer.
Everyone at the same time- wait until I say, “1, 2, 3 UP!” to put up your answer.
Use your notes to help you!

26. Checking for Understanding
LecturePLUS Timberlake 99
Checking for Understanding
1. When you touch ice, heat is transferred
from
A) your hand to the ice
B) the ice to your hand

27. Checking for Understanding
2. When you drink a hot cup of coffee, heat
is transferred from
A) your mouth to the coffee
B) the coffee to your mouth

28. Checking for Understanding
LecturePLUS Timberlake 99
Checking for Understanding
3. When you heat 200 g of water for 1 minute, the water temperature rises from 10°C to 18°C.
If you heat 400 g of water at 10°C in the same pan with the same amount of heat for 1 minute, what would you expect the final temperature to be?
A) 10 °C B) 14°C C) 18°C
400 g
200 g

29. Checking for Understanding- Ansswer
LecturePLUS Timberlake 99
Checking for Understanding- Ansswer
B)14°C
Heating twice the mass of water using the same amount of heat will raise the temperature only half as much.
400 g
200 g

30. Checking for Understanding
LecturePLUS Timberlake 99
Checking for Understanding
4. A substance with a large specific heat
A) heats up quickly B) heats up slowly
B) heats up slowly
5. When ocean water cools, the surrounding air
A) cools B) warms C) stays the same
B) warms

31. Checking for Understanding
LecturePLUS Timberlake 99
Checking for Understanding
6. Sand in the desert is hot in the day, and cool
at night. Sand must have a
A) high specific heat B) low specific heat
B) low specific heat

32. Example of Heat Calculations
LecturePLUS Timberlake 99
Example of Heat Calculations
A hot-water bottle contains 750 g of water at 65°C. If the water cools to body temperature (37°C), how many calories of heat could be transferred to sore muscles?
heat = g x T x C. (H2O)
750 g x 28°C x cal g°C
= cal

33. Checking for Understanding
LecturePLUS Timberlake 99
Checking for Understanding
7. How many kcal are needed to raise the temperature of 120 g of water from 15°C to 75°C?
A) 1.8 kcal
B) 7.2 kcal
C) 9.0 kcal
120 g x (75°C - 15°C) x 1.00 cal x 1 kcal
g°C cal

34. Experimentation Research about hand warmers. Read the instructions.
Prepare the materials.
Record observations and data based on the first reaction
Carry out the other four reactions.
Collect and record your data in tables.
Analyze and interpret your data.

35. CHALLENGE – Engineering Practices
Do you remember the introduction to this unit? We talked about the Fishermen in very cold areas. Your task is to use the calorimetry principles you have learned to create the most effective hand warmer. For this purpose, you will test different reactions in separate calorimeters.

36. Essential Questions
Claim (statement), evidence to support it (relevant and sufficient data) and a reasoning.
How do you distinguish between exothermic and endothermic reactions?
What is the relationship or pattern between the values for C and the enthalpy in chemical process?
Claim
Evidence
Reasoning

37. Engineering Practices

38. Engineering Practices- Challenge Efficient hand warmers
Defining and delimiting the problem- Designing solutions to reduce the impact of the constrains and limits.
 Carry out your test.
Optimize the design solution.
Dispose