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What’s the MATTER: Specific Heat of Matter

What’s the MATTER: Specific Heat of Matter. Matter, Specific Heat of Matter At the conclusion of our time together, you should be able to:. Define specific heat Use specific heat to determine energy changes. Exothermic and Endothermic Processes.

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What’s the MATTER: Specific Heat of Matter

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  1. What’s the MATTER:Specific Heat of Matter

  2. Matter, Specific Heat of Matter At the conclusion of our time together, you should be able to: Define specific heat Use specific heat to determine energy changes

  3. Exothermic and Endothermic Processes • Essentially all chemical reactions and changes in physical state involve either: • release of heat, or • absorption of heat

  4. Exothermic and Endothermic Processes • In studying heat changes, think of defining these two parts: • the system - the part of the universe on which you focus your attention • the surroundings - includes everything else in the universe

  5. Exothermic and Endothermic Processes • Together, the system and it’s surroundings constitute the universe • Thermochemistry is concerned with the flow of heat from the system to it’s surroundings, and vice-versa.

  6. Exothermic and Endothermic Processes • Heat flowing out of a system into it’s surroundings: • defined as negative • q has a negative value • called exothermic • system loses heat (gets cooler) as the surroundings heat up

  7. Exothermic and Endothermic Processes • Heat flowing into a system from its surroundings: • defined as positive • q has a positive value • called endothermic • system gains heat (gets warmer) as the surroundings cool down

  8. Energy Transformations • Heat - represented by “q”, is energy that transfers from one object to another, because of a temperature difference between them. • only changescan be detected! • flows from warmer  cooler object

  9. Units for Measuring Heat Flow • A calorie is defined as the quantity of heat needed to raise the temperature of 1 g of pure water 1 oC. • Used except when referring to food • a Calorie, (written with a capital C), always refers to the energy in food • 1 Calorie = 1 kilocalorie = 1000 cal.

  10. Units for Measuring Heat Flow • The calorie is also related to the Joule, the SI unit of heat and energy • named after James Prescott Joule • 4.184 J = 1 cal • Heat Capacity - the amount of heat needed to increase the temperature of an object exactly 1 oC • Depends on both the object’s mass and its chemical composition

  11. Heat Capacity and Specific Heat • Specific Heat Capacity(abbreviated “C”) - the amount of heat it takes to raise the temperature of 1 gram of the substance by 1 oC • often called simply “Specific Heat” • Water has a HUGE value, when it is compared to other chemicals

  12. Note the tremendous difference in Specific Heat. Water’s value is VERY HIGH.

  13. Heat Capacity and Specific Heat • For water, C = 4.18 J/(g oC) in Joules, and C = 1.00 cal/(g oC) in calories. • 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!

  14. Heat Capacity and Specific Heat • To calculate, use the formula: q = mass (in grams) x T x C • heat is abbreviated as “q” • T = change in temperature • C = Specific Heat • Units are either: J/(g oC) or cal/(g oC)

  15. Practice #1 • q = cp x m x t: • q = 59.912 J • cp = x • m = 36.359 g • t = 152.0 oC 59.912 J = (x)(36.359 g)(152.0 oC) = 0.01084 J/goC

  16. Practice #2 • q = cp x m x t: • q = -800. J • cp= 0.4210 J/g oC • m = 73.174 g • t = (x – 102.0 oC) -800. J = 0.4210 J/goC (73.174 g)(x – 102.0 oC) -800. = 30.81x – 3142 2342 = 30.81x = 76.0 oC

  17. Matter, Specific Heat of Matter Let’s see if you can : Define specific heat Use specific heat to determine energy changes

  18. Define Specific Heat • Specific Heat – the amount of energy required to raise the temperature of one gram of a substance by one Celsius degree or one Kelvin

  19. Practice #3 • q = cp x m x t: • q = -185.4 J • cp= 0.440 J/g oC • m = x g • t = -1475 oC -185.4 J = (0.440 J/goC )(x)(-1475 oC) -185.4 J = -649 Jg = 0.29 g

  20. Practice #4 • q = cp x m x t: • q = x J • cp= 0.0335 cal/goC (4.184 J/cal) • m = 152.00 g • t = -51.5oC x = (0.140164 J/goC )(152.00 g)(-51.5 oC) = -1.10 x 103 J

  21. Calorimetry • Calorimetry - the measurement of the heat into or out of a system for chemical and physical processes. • Based on the fact that the heat released = the heat absorbed • The device used to measure the absorption or release of heat in chemical or physical processes is called a “Calorimeter”

  22. Calorimetry • Foam cups are excellent heat insulators, and are commonly used as simple calorimeters under constant pressure. • For systems at constant pressure, the “heat content” is the same as a property called Enthalpy (H) of the system (They are good because they are well-insulated.)

  23. A foam cupcalorimeter – here, two cups are nestled together for better insulation

  24. Calorimetry • Changes in enthalpy = H • q = H These terms will be used interchangeably in this textbook • Thus, q = H = m x C x T • H is negative for an exothermic reaction • H is positive for an endothermic reaction

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