1 Heat Energy “how we recognize that there were heat energy transferred between two substances”

2 Heat Energy that flows from something warm to something cooler A hotter substance gives KE to a cooler one When heat is transferred (lost or gained), there is a change in the energy within the substance

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 °C2) 14°C 3) 18°C 200 g 400 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. 200 g 400 g

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

7 Specific Heat 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 Different substances have different capacities for storing energy It may take 20 minutes to heat water to 75°C. However, the same mass of aluminum might require 5 minutes and the same amount of copper may take only 2 minutes to reach the same temperature.

9 Specific Heat Values Specific heat is the a mount of heat needed to raise the temperature of 1 g of a substance by 1°C cal/g°CJ/g°C water aluminum copper silver gold

10 Learning Check A. A substance with a large specific heat 1) heats up quickly2) heats up slowly B. When ocean water cools, the surrounding air 1) cools 2) warms3) 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 2) low specific heat

11 Solution A. A substance with a large specific heat 2) heats up slowly B. When ocean water cools, the surrounding air 2) warms C. Sand in the desert is hot in the day, and cool at night. Sand must have a 2) low specific heat

12 Measuring Heat Requires Temperature change  T Grams of substance Specific heat of the substance

Bagaimana mengukur derajat panas sebuah benda? We have to use Thermometer. 13 Thermometers commonly have alcohol (with dye) or mercury Digital thermometers have replaced older ones Celsius is the metric scale for measuring temperature Water freezes at 0 º C and boils at 100ºC What is the commonly scale for Thermometer?

14 The Kelvin scale is a metric temperature scale measured in Kelvin units (K) Formula (273+ºC)= Kelvin Kelvin scale Question: What is the boiling point of water on the Kelvin scale? What is the freezing point of water on the Kelvin scale?

15 Absolute zero Means that : The temperature in which all molecular motion stops (0 K) Question : What is absolute zero on the Celsius scale?

16 Calculating Heat, Q mass x temp. change x specific heat m x  T x c

17 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 = m x  T x Sp. Ht. (H 2 O) = 750 g x 28°C x 1.00 cal g°C = cal

18 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

19 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

20 Energy and Nutrition 1 Calorie (nutritional) = 1 kcal 1 Cal= 1000 cal

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

22 Foods and Calories FoodCarboFatProtein Energy(kcal) carrots, 1 cup banana egg chicken (no skin) beef (3 oz)

23 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

24 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

25 Q = m L A phase change is a physical change that requires a change in heat energy Example: the change of ice into water Energy needed to change the phase of the substance that is of mass m, is Q Heat and Phase Changes dengan L = kalor lebur (cal/gr)

Questions What is freezing point, melting point, and boiling point?

What is a calorimeter? Device used to measure the heat given off during chemical reactions