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Thermodynamics Ch. 21 to 24. Heat Heat is the energy that flows because of temperature differences. Temperature is a measure of the internal energy of.

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Presentation on theme: "Thermodynamics Ch. 21 to 24. Heat Heat is the energy that flows because of temperature differences. Temperature is a measure of the internal energy of."— Presentation transcript:

1 Thermodynamics Ch. 21 to 24

2 Heat Heat is the energy that flows because of temperature differences. Temperature is a measure of the internal energy of a substance.

3 Thermal Contact When heat flows from one object to another that it is in contact with, this is called thermal contact. When thermal contact exists, heat flows from the higher temperature substance (warmer one) to the lower temperature substance (cooler one).

4 HEAT FLOWS ACCORDING TO TEMPERATURE DIFFERENCES FROM HOT TO COLD

5 Thermal Equilibrium Equilibrium means balance. After objects in thermal contact with each other reach the same temperature, no heat flows between them. They are considered to be in thermal equilibrium.

6 Energy Potential energy represents the forces between molecules. Kinetic energy represents moving atoms within the molecules. The grand total of all energies inside a substance is called internal energy.

7 SUBSTANCES DO NOT CONTAIN HEAT, THEY CONTAIN ENERGY.

8 Measuring Heat The calorie is the amount of heat required to raise the temperature of 1 gram of water by 1ºC. A kilocalorie or kCal is 1000 calories. When they use the term calorie on food labels, they actually mean a kCal.

9 Calories Again, this is a measurement only used in the United States. Everywhere else uses the Joule or the kilojoule (kJ). 1 calorie = 4.184 Joule

10 Calories The energy value of food is determined by burning the food and measuring the energy that is released as heat.

11 Heat Capacity Water has a higher capacity for storing energy than most common materials. We say water has a high specific heat. This makes water a good cooling agent. Water takes longer to cool down.

12 Heat Gases expand and contract more than liquids. (Molecules are more free to move.) Liquids expand and contract more than solids for the same reason.

13 The math of thermo… 1 liter of water @ 30°C is mixed with 1 liter of water @ 20°C. What is the final temperature of the mixture?

14 The equation…. T 1 V 1 + T 2 V 2 = T 3 V 3

15 The solution… T 1 V 1 + T 2 V 2 = T 3 V 3 (30 x 1.0) + (20 x 1.0) = (T x 2.0) 30 + 20 = 2T 50 = 2T T = 25 °C

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