Energy and Heat Flow Essay

The study of occur during chemical reactions AND changes of state. Heat: Variable = unit: Define: Common Units: Heat always flows from a object. Example: When looking at heat flow we use the terms System Surroundings object to a changes that and Endothermic vs.. Exothermic Reactions and Processes: Definition: Exothermic Endothermic Sign of q What happens to system What you feel (the surroundings) Examples Place in chemical reaction How heat flow is measured: You need to know the following conversions: Calories vs.. Calories: In the chemistry lab we use calories when measuring heat flow.

The Calories that you find on your food labels are equal to 1000 calories. Example 1: Convert 605 calories to Joules. Convert 950 Calories to calories. Heat Capacity and Specific Heat: Some definitions: calorie: The quantity to neat required to raise the temperature to by 1 co. Heat capacity: The quantity of heat required to raise the temperature of quantity of heat required to raise the temperature of co. Examples: Concrete vs.. Water by 1 co. Specific Heat (C): The by 1 There are 4 types of problems you will be responsible for this chapter.

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Type 1 : Calculating heat (q) or specific heat (C) when there is a process with a temperature change. Key words: “temperature is raised from cot “temperature is raised by Common specific heat values: Ice = 2. 1 J/egg Coater=4. 18 J/egg or 1 cal/egg Steam=l . 7 J/egg co. ” or Examples: 1. When 435 J of heat is added to 3. 4 grams of olive oil at 21 co, the temperature increases to 85 co. What is the specific heat of olive oil? 2. How much heat is required to raise the temperature of 250. 0 g of mercury by 52 co? (see text for specific heat values).

Thermoelectric Equations: Chemical equations that include heat In a chemical reaction, heat is either absorbed (_) or released Enthalpy: The measurement of heat at constant pressure. Essentially it is equal to q. Symbol: equation: Exothermic: Endothermic: . Writing heat in a chemical Type 2: Calculating heat when there is a chemical reaction (reaction given in problem). Key words in problem: given a chemical equation: How to solve: Use geochemistry! 0 Examples: 1 . When one mole of carbon disulfide is formed from its elements, 89. 3 k of heat is absorbed.

Calculate the amount of heat (in k) when 5. 66 g of formed. C(s) + AS CSS 89. 3 k 2. Given the reaction Effie + CO 0 2 Fee + 3 CO + 26. 3 k], how many k of heat are produced when 3. 40 moles of CO are reacted with excess Effie? Calculating the heat of phase changes (melting, freezing, vaporizing, condensing) An ice cube melts because it absorbs heat from the environment which causes it to convert from solid water to liquid water. During this time there is no change in temperature the temperature will only increase once all of the ice has been converted to liquid water.

Molar heat of fusion (Fuss ) is the heat absorbed by to a substance in melting trot a solid too liquid d. Molar neat to solidification (Solid ) is the heat lost when one mole of a liquid solidifies at constant temperature. How they are related: Molar heat of vaporization (Pave) and molar heat of condensation (Second) are related in the same way.

Heat is energy that transfers from one object to another because they are at the same temperature. D. Gasoline contains a significant amount of chemical potential energy. 4. Circle the letter next to each sentence that is true about heat. A. One effect of adding heat to a substance is an increase in the temperature of that substance. B. Heat always flows from a cooler object to a warmer object. O Prentice- Hall, Inc. C. If two objects remain in contact, heat will flow from the warmer object to the cooler object until the temperature of both objects is the same. Exothermic and Endothermic Processes (pages 294-295) 5.

What can be considered the “system” and what are the “surroundings” when studying a mixture of chemicals undergoing a reaction? Write your answers where indicated below. System: Surroundings: Guided Reading and Study Workbook CHAPTER 1 1, Thermometric?Heat and Chemical Change (continued) 6. In thermoelectric calculations, is the direction of heat flow given from the point of view of the system, or of the surroundings? . What universal law states that energy can neither be created nor destroyed and can always be accounted for as work, stored potential energy, or heat?

Questions 8 through 12 refer to the systems and surroundings illustrated in diagrams (a) and (b) below. Heat (a) (b) heat 8. Which diagram illustrates an endothermic process? 9. Is heat flow positive or negative in diagram (a)? 10. Which diagram illustrates an exothermic process? 11. Is heat flow positive or negative in diagram (b)? 12. What does a negative value for heat represent? To answer Questions 13 and 14, look at Figure 1 1. On page 295. 13. A system is a person sitting next to a campfire. Is this system endothermic or exothermic? Explain why. O Prentice-Hall, Inc. 14.

A system is a person who is perspiring. Is this system endothermic or exothermic? Explain why. 102 Guided Reading and Study Workbook Heat Capacity and Specific Heat (pages 295-297) 15. Heat generated by the human body is usually measured in units called . 16. Describe the chemical reaction that generates heat in the human body. 17. What is the definition of a calorie? 18. How is the calorie (written with a lower case c) related to the dietary Calorie written Witt a capita 19. Circle the letter next to the SSL unit of heat and energy. A. Calorie b. Calorie c. Joule d. Celsius degree 20.

Is the next sentence true or false? Samples of two different substances having the same mass always have the same heat capacity. 21 . Compare the heat capacity of a 2-keg steel frying pan and a 2- g steel pin. If the heat capacities of these objects differ, explain why. 22. Is the next sentence true or false? The specific heat of a substance varies with the mass of the sample. This section explains how to construct equations and perform calculations that show heat changes for chemical and physical processes.

Calorimeter (pages 300-303) 1. The property that is useful for keeping track of heat changes in chemical and physical processes at constant pressure is called calorimeter? . 2. What is 103 CHAPTER 1 1, Thermometric?Heat and Chemical Change (continued) 3. Use Figure 1 1. 8 on page 300. Circle the letter next to each sentence that is true about calorimeters. A. The calorimeter container is insulated to minimize loss of heat to or absorption of heat from the surroundings. B. Because foam cups are excellent heat insulators, they may be used as simple calorimeters.