1. Thermodynamics

2. Energy in general is the ability to cause a change. In chemistry, energy can do work or produce heat. Energy is typically divided into two types: potential energy and kinetic energy. Potential energy is stored energy in the form of position (gravity-related, like a skateboarder at the top of a half-pipe) or chemical composition (like the chemicals in food or a battery). Kinetic energy is energy of motion, and is the usual use for potential energy (food energy allows you to move).

3. Energy can be converted between kinetic energy and potential energy, even several times, but no matter how many times energy is converted the Law of Conservation of Energy states that no energy can be lost or created.

4. The energy stored in a substance because of the atoms that make it up is chemical potential energy. For example, when octane (C 8 H 18 ) is placed into an automobile’s gas tank, it can be burned later to move the automobile. Unfortunately a lot of the chemical potential energy in gasoline is “lost” in the engine as heat, so it is not available for motion. Heat

5. Heat Energy Heat (symbolized q) is the energy that naturally moves from something hot to something cold. The amount of heat is often measured as temperature, but temperature does not directly measure heat. For example, water at 20 °C does not have twice as much heat as water at 10 °C, but it does have more heat!

6. To measure heat directly, the calorie (abbreviated cal) was defined as the amount of heat needed to increase the temperature of 1 gram (1 milliliter) of water by 1 °C. Note that the Calories reported on food wrappers are the measurement for heat to increase the temperature of 1000 grams (one liter) of water by 1 °C, in other words a kilocalorie.

7. The measurement of how much heat energy can come from food is called calorimetry.

8. Calories are still used in the nutrition field, but in chemistry we will use the Joule (abbreviated J). There are 4.184 Joules in 1 calorie. Not everything heats up at the same rate. The rate at which things heat is called the specific heat (abbreviated c p ).

9. When a cake has been baked and is removed from the oven it would cause severe burns to touch the metal pan, but often the top of the cake is touched to test if the cake is ready. The metal of the pan has a low specific heat so it can lose heat quickly (which would be absorbed by your finger) and the cake contains a lot of trapped air and other material with a higher specific heat which lose heat slowly, allowing more time before your finger has absorbed enough heat to cause a burn. -Summary – High Specific Heat = hard to heat

10. In total, to calculate the amount of heat that can be gained or lost by an object the formula is q = m × c p × ∆T q = heat, measured in J m = mass, measured in g c = specific heat, measured in ∆T = Temperature final – Temperature initial, measure in °C J g °C

11. What is the heat absorbed by 100 g of water to raise it from 25 °C to 75 °C? The specific heat of water is 4.184 J/g°C. (this is heating so it will be positive) q = m × c p × ∆T q = _100 g__ x _4.184 J/g°C_ x (_75 °C_ - _25 °C _) q = _20920 J_

12. What is the heat given off by 100 g of iron to cool from 50 °C to 20 °C? The specific heat of iron is 0.449 J/g°C. (this is cooling so it will be negative) q = m × c × ∆T q = _100 g__ x _.449 J/g°C_ x (_20 °C_ - _50 °C _) q = _-1347 J_

13. Heat Movement The Law of Conservation of Energy reminds us that heat energy cannot just appear out of nowhere and disappear to nowhere, so if an object warms up, then that heat had to be absorbed from somewhere and if an object cools down, then that heat had to be given off to something.

14. Heat can move from one object to another by three ways: convection, conduction, and radiation.

15. Conduction is the movement of heat between objects that are touching. Examples: steak on a hot grill Convection is the movement of heat by circulating fluids (gas or liquid). Examples: air-conditioners, ocean currents, and the warm and cold “fronts”. Radiation, is the movement of heat by electromagnetic waves (which can move through space). Examples: infrared waves, fire, the coil in an electric oven.

16. Phases and Changes Memorize the names of the phase changes. Notice that q is positive for heating and negative for cooling

17. A heat curve shows that as heat is added temperature increases. However at the point of a phase change it takes a certain amount of heat before the temperature will rise again. You have to add this heat in if you are warming or subtract if cooling.

18. so new equations are needed for use during a phase change: during melting/freezing, q = m × H f during boiling/condensing, q = m × H v q = heat (subtract if cooling), measured in J m = mass, measured in g H f = heat of fusion, measured in H v = heat of vaporization, measured in J g J g

19. Calculate the heat needed to heat 100 g of water from -40 °C to 140 °C. Since the specific heat depends on the state of matter, you have to calculate the heat up to the melting point, the melting point, up to the boiling point, the boiling point, and then past the boiling point. H f water = 334 J/gH v water = 2260 J/g c p ice = 2.06 J/g °C c p water = 4.18 J/g °C c p steam = 1.87 J/g °C

20. Step 1: Ice from -40 °C to 0 °C. q = m × c p × ∆T q = _100g_ x _2.06 J/g °C x (_0 °C - _-40 °C_) q = _8240 J_ Step 2: Turning ice into liquid water q = m × H f q = 100 g x 334 J/g q = 33400

21. Step 3: Water from 0 °C to 100 °C. q = m × c p × ∆T q = _100g_ x _4.184 J/g °C x (_100 °C - _0 °C_) q = _41840 J_ Step 4: Turning liquid water into steam. q = m × H v q = 100 g x 2260 J/g q = 226000 g_

22. Step 5: Steam (Water vapor) from 100 °C to 140 °C q = m × c p × ∆T q = _100g_ x _1.87 J/g °C x (_140 °C - _100 °C_) q = _7480 J_ Total heat involved = _8240 J_ + _33400 J_ + _41840 J_ + _226000 J_ + _7440 J_ Total heat = _316960 J_

23. Heat and Chemical Reactions Chemical reactions should be written with heat as a reactant or a product. If a chemical reaction feels cold when it is happening, then the reaction is absorbing heat and we call it endothermic. If a chemical reaction feels warm when it is happening, then it is giving off heat and we call it exothermic.

24. In both endothermic and exothermic chemical reactions, the energy does not need to be heat only. Light and electricity are other examples of energy. If it uses energy it is endothermic, if it gives it off it is exothermic.