Thermochemistry - concerned with heat changes that occur during chemical reactions

1. Thermochemistry - concerned with heat changes that occur during chemical reactions

2. Heat, q • energy that transfers from one object to another, because of a temperature difference between them • Energy that flows from something warmer to something cooler

3. Learning Check A. When you touch ice, heat is transferred from 1) your hand to the ice 2) the ice to your hand B. When you drink a hot cup of coffee, heat is transferred from 1) your mouth to the coffee 2) the coffee to your mouth

4. Learning Check 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? 1) 10 °C 2) 14°C 3) 18°C 400 g 200 g

5. Solution 2)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

6. Some Equalities for Heat Heat is measured in calories or joules • 1 kcal = 1000 calorie • 1 Calorie = 1000 calorie • 1 calorie = 4.18 J • 1 kJ = 1000 J

7. Specific Heat Capacity • Why do some foods stay hot longer than others? • Why is the beach sand hot, but the water is cool on the same hot day?

8. Specific Heat Capacity the amount of heat energy needed to raise the temperature of 1 g of a substance by 1°C cal/g-°C water 1.00 aluminum 0.22 copper 0.093 Substances with low specific heat capacities requires ________(more or less?) energy to feel hot than those with high specific heat capacities At the same mass and amount of heat added, substances with low specific heat capacities will be ________(hotter or cooler?) than those with high specific heat capacities less

9. 26 oC 26 oC 29 oC 36 oC 26 oC

10. Specific Heat Capacity At the same mass and amount of heat, substances with low specific heat capacities will be ________(hotter or cooler?) than those with high specific heat capacities hotter

11. Water has a HUGE value, compared to other chemicals • For water, C = 4.18 J/(g oC), and also C = 1.00 cal/(g oC) • Thus, for water: • it takes a long time to heat up, and • it takes a long time to cool off! • Water is used as a coolant!

12. Learning Check A. A substance with a large specific heat capacity 1) heats up quickly 2) heats up slowly B. When ocean water cools, the surrounding air 1) cools 2) warms 3) stays the same C. Sand in the desert is hot in the day, and cool at night. Sand must have a 1) high specific heat capacity 2) low specific heat capacity

13. Calculating Heat, q mass x temp. change x specific heat capacity m x T x C

14. Molar heat capacity, ΔH • Amount of heat energy required to increase the temperature of one mole of a substance by one Kelvin • ΔH = CΔT

15. Heat Calculations A hot-water bottle contains 750 mL 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 = m x T x Sp. Ht. (H2O) = 750 g x 28°C x 1.00 cal g - °C = 21 000

16. Learning Check How many kcal are needed to raise the temperature of 120 g of water from 15°C to 75°C? 1) 1.8 kcal 2) 7.2 kcal 3) 9.0 kcal

17. Solution How many kcal are needed to raise the temperature of 120 g of water from 15°C to 75°C? 2) 7.2 kcal 120 g x (75°C - 15°C) x 1.00 cal x 1 kcal g - °C 1000 cal

18. Calorimeter • a device used to measure heat energy • can be used to measure the specific heat capacity of materials by measuring the water’s temperature change as a warm object is placed in the calorimeter

19. Energy and Nutrition a Calorie, written with a capital C, always refers to the energy in food 1 Calorie (nutritional) = 1 kcal 1 Cal = 1000 cal

20. Caloric Food Values Carbohydrate = 4 kcal/g Fat = 9 kcal/g Protein = 4 kcal/g

21. Foods and Calories Food Carbo Fat Protein Energy(kcal) carrots, 1 cup 11g 0g 1g 48 banana 26 0 1 108 egg 0 6 6 78 beef (3 oz) 0 5 22 133

22. Learning Check 1.0 cup of whole milk contains 12 g of carbohydrate, 9.0 g of fat, and 9.0 g of protein. How many kcal (Cal) are obtained? 1) 48 kcal 2) 81 kcal 3) 165 kcal

23. Solution 3) 165 kcal 12 g carbo x 4 kcal/g = 48 kcal 9.0 g fat x 9 kcal/g = 81 kcal 9.0 g protein x 4 kcal/g = 36 kcal Total kcal = 165 kcal