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Understanding Energy Measurement: Kinetic Theory and Specific Heat Capacity

This overview covers the fundamental concepts of energy measurement, focusing on kinetic theory and the specific heat capacity of substances. It explains how energy is related to motion, highlighting that all substances have kinetic energy due to molecular motion, even at temperatures above absolute zero. Additionally, the document elaborates on how different materials react to heat, demonstrating this through examples of water, metals, and glass. The specific heat capacity is defined and a calculation example is provided to illustrate how to determine heat transfer in real-life situations.

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Understanding Energy Measurement: Kinetic Theory and Specific Heat Capacity

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  1. Energy-further topics How will we measure energy?

  2. Kinetic Theory of Molecular Motion • Absolute zero- The absence of motion, and therefore the absence of kinetic energy. • If the temperature of any substance is above absolute zero, then there must be motion (and heat). • All substances are in motion, even solids. • Kinetic energy of a system is the result of collisions between molecules. • Temperature is the measure of the average kinetic energy of a system (a body, a block of wood, the atmosphere)

  3. The measurement of energy • You have observed how different materials react to energy differently • Metals transfer heat rapidly • Water reacts to heat more slowly • Glass tends to retain heat

  4. Specific Heat Capacity ( c ) • The way a substance responds to energy is specific and unique to that substance: i.e., a characteristic property. • Definition: The amount of heat necessary to raise one gram of the substance 1°C • Reported in J/g-°C or cal/g-°C

  5. The measurement of energy II • You may have noticed that a large pot of water tends to take longer to boil than a small pot • You may have also noticed that a large block of ice takes much longer to melt than a small ice cube • You may have noticed that a pot of hot water takes much less time to boil than a pot of cold water • What does this mean?

  6. The measurement of energy III • The way a substance responds to energy is also dependent on the amount of substance present; i.e., its mass • We can calculate the amount of energy transferred by measuring the change in temperature.

  7. Putting it all together • The heat contained in a substance can be calculated by applying the following equation: • Heat content (q) = • mass • x specific heat capacity • x change in temperature • Or q = m x c x Dt (D means “change in”) • Simpler form q = mcDt

  8. Calorimetry • If q = mcDt, then we can manipulate this relationship to determine all other quantities in the relationship. • m = q/cDt • c = q/mDt • Dt = q/mc • If we know 3, the fourth can be calculated.

  9. Sample Problem • How much heat was transferred to 200.0g of water if its temperature increased by 15.0°C? • The specific heat capacity of water is 4.184J/g-°C • Q = mcDt so: • 200g x 4.184J/g-°C x 15°C = • 12552J or 12600J

  10. Assignment • Heat problem set due Thursday 9/16 • Heat transfer lab Friday 9/17

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