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The Flow of Energy – Heat. Chapter 17.1. Warm Up. What happens to the heat from the lava?. Why does lava cool more quickly in water than on land?. Introduction to Thermochemistry.

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Presentation Transcript

Warm up
Warm Up

What happens to the heat from the lava?

Why does lava cool more quickly in water

than on land?


Introduction to thermochemistry
Introduction to Thermochemistry

  • Thermochemistry (or Thermodynamics) is the study of heat, energy, and temperature changes that occur during chemical reactions (One of the main courses of study in Physical Chemistry)

  • Law of Conservation of Energy (1st Law of Thermodynamics) – The law of conservation of energy states that energy may neither be created nor destroyed. Therefore the sum of all the energies in the system is a constant. (Whether a reaction flask or the universe


Temperature vs heat
Temperature vs. Heat

  • Temperature is the measure of the average kinetic energy of the particles in a substance

    • Measure using a thermometer

    • Rises when heat is added

    • Falls when heat is removed

  • Heat(q) is the energy that is transferred between two objects

    • Cannot be measured directly

    • Can only detect the changes caused by heat

HOT

COLD


Thermochemical reactions
Thermochemical Reactions

  • System – reactants and products

  • Surroundings – the reaction container


Exothermic vs endothermic
Exothermic vs. Endothermic

Exothermic

Endothermic

Heat

Heat


Measuring heat
Measuring Heat

  • The Joule (J) is the SI unit of heat and energy

  • The calorie (cal) is also used to measure heat capacity and is defined by the amount of heat needed to raise the temperature of 1g of pure water by 1C

  • 1 J = 0.2390 cal 1 cal = 4.184 J

  • NOTE: The energy contained in food is measured in Calories (Cal) = 1000 calories = 1 kcal


Heat capacity vs specific heat
Heat Capacity vs Specific Heat

  • Heat capacity is the amount of heat needed to raise the temperature of a substance by 1C

    J/C or J/K

  • Specific heat capacity (C) is the amount of heat needed to raise the temperature of one gram of a substance by 1C

    J/gC or J/gK



Cool down
Cool Down

Which of these pictures contains more heat?

C = q / m xDT

q = C x m xDT


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