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Thermodynamics – study of energy First law of thermodynamics Energy of the universe is constant

Thermodynamics – study of energy First law of thermodynamics Energy of the universe is constant Energy can not be created or destroyed. Energy is the ability to do work or produce heat. 2 types of Energy. Kinetic energy Energy of motion E = ½ mv 2. Potential energy

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Thermodynamics – study of energy First law of thermodynamics Energy of the universe is constant

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  1. Thermodynamics – study of energy • First law of thermodynamics • Energy of the universe is constant • Energy can not be created or destroyed

  2. Energy is the ability to do work or produce heat. • 2 types of Energy Kinetic energy Energy of motion E = ½ mv2 Potential energy Energy of position

  3. Law of conservation of energy • Energy can not be created or destroyed but can be converted from one form to another • Ex chemical energy (gas) can be converted to mechanical and thermal energy

  4. Internal energy = E “sum” of kinetic & potential energies of all “particles” in a system Internal energy can be transferred by two types of energy flow: • Heat (q) (q = quantity of heat) • Work (w) E = q + w Change of energy in a system

  5. Measuring Energy Changes • common energy units for heat are the calorie and the joule. • Calorie – the amount of energy (heat) required to raise the temperature of one gram of water 1oC. • Joule – heat required to raise the temperature of 1 g of water by 0.24 K 1 calorie = 4.184 joules

  6. System – part of the universe on which we focus attention • Surroundings – everything else in the universe • Ex. Burning a match is the system releases heat to surroundings

  7. Endothermic – energy flows into system Exothermic – energy flows out of system

  8. C- Specific heat capacity energy required to change the mass of one gram of a substance by one degree Celsius. [joule/gram °C] • Like energy storage bank

  9. C- Specific heat capacity energy required to change the mass of one gram of a substance by one degree Celsius. [joule/gram °C] • Like energy storage bank • Water has a high specific heat capacity that means it takes a lot of heat (joules) to increase the temperature of water compared to metals (water better at storing energy than metals

  10. B. Measuring Energy Changes • To calculate the energy required for a reaction: Q = C  m t

  11. Q = C  m t How much heat is required to warm 145 g of water from 25 *C to 65 *C

  12. Q = m x C t How much heat is required to warm 145 g of water from 25 *C to 65 *C the specific heat of liquid water is 4.184 J/g *C Q = m x C t Q = 145 g x 4.184 J x (65 *C - 25 *C) g *C

  13. Q = m x C t How much heat is required to warm 145 g of water from 25 *C to 65 *C the specific heat of liquid water is 4.184 J/g *C Q = C  m t Q = 145 g x 4.184 J x (65 *C - 25 *C) g *C Q = 145 x 4.184 J x 40 Q = 24,267 joules

  14. A quantity of water is heated from 20.0 *C to 48.3 *C by absorbing 623 Joules of heat energy, what is the mass of the water? Specific heat of water is 4.184 J/g *C Q = C  m t __Q__ = m C x t

  15. A quantity of water is heated from 20.0 *C to 48.3 *C by absorbing 623 Joules of heat energy, what is the mass of the water? Specific heat of water is 4.184 J/g *C Q = C  m t __Q__ = m C x t 623 J = m 4.184 J /g *C x (48.3 *C - 20 *C)

  16. A quantity of water is heated from 20.0 *C to 48.3 *C by absorbing 623 Joules of heat energy, what is the mass of the water? Specific heat of water is 4.184 J/g *C Q = C  m t __Q__ = m C x t 623 J = m 4.184 J /g *C x (48.3 *C - 20 *C) 623 J = m 4.184 J /g *C x (28.3 *C) 5.26 g = m

  17. In a household radiator a 25.5 g of steam at 100 *C condenses (changes from gas to liquid) How much heat is released? Heat of vaporization is 2260 J/g Q = m Hvap

  18. In a household radiator a 25.5 g of steam at 100 *C condenses (changes from gas to liquid) How much heat is released? Heat of vaporization is 2260 J/g Q = m Hvap Q = 25.5 g x 2260 J/g Q = 57,630 J

  19. Objectives • To consider the heat (enthalpy) of chemical reactions • To understand Hess’s Law

  20. A. Thermochemistry (Enthalpy) • Enthalpy, H– energy function • At constant pressure H is equal to the energy that flows as heat. Hp = heat = q ΔH = q  (valid for constant pressure ONLY!)

  21. A. Thermochemistry Calorimetry • Enthalpy, H is measured using a calorimeter.

  22. B. Hess’s Law • For a particular reaction, the change in enthalpy is the same whether the reaction takes place in one step or a series of steps. • Example: N2(g) + 2O2(g) 2NO2(g)H1 = 68 kJ

  23. Objectives • To understand how the quality of energy changes as it is used • To consider the energy resources of our world • To understand energy as a driving force for natural processes

  24. A. Quality Versus Quantity of Energy • When we use energy to do work we degrade its usefulness.

  25. A. Quality Versus Quantity of Energy • Petroleum as energy

  26. B. Energy and Our World • Fossil fuel – carbon based molecules from decomposing plants and animals • Energy source for United States

  27. B. Energy and Our World • Petroleum – thick liquids composed of mainly hydrocarbons • Hydrocarbon – compound composed of C and H

  28. B. Energy and Our World • Natural gas – gas composed of hydrocarbons

  29. B. Energy and Our World • Coal – formed from the remains of plants under high pressure and heat over time

  30. B. Energy and Our World • Effects of carbon dioxide on climate • Greenhouse effect

  31. B. Energy and Our World • Effects of carbon dioxide on climate • Atmospheric CO2 • Controlled by water cycle • Could increase temperature by 10oC

  32. B. Energy and Our World • New energy sources • Solar • Nuclear • Biomass • Wind • Synthetic fuels

  33. C. Energy as a Driving Force • Natural processes occur in the direction that leads to an increase in the disorder of the universe. • Example: • Consider a gas trapped as shown

  34. C. Energy as a Driving Force • What happens when the valve is opened?

  35. C. Energy as a Driving Force • Two driving forces • Energy spread • Matter spread

  36. C. Energy as a Driving Force • Energy spread • In a given process concentrated energy is dispersed widely. • This happens in every exothermic process.

  37. C. Energy as a Driving Force • Matter spread • Molecules of a substance spread out to occupy a larger volume. • Processes are favored if they involve energy and matter spread.

  38. C. Energy as a Driving Force • Entropy, S – function which keeps track of the tendency for the components of the universe to become disordered

  39. C. Energy as a Driving Force • What happens to the disorder in the universe as energy and matter spread?

  40. C. Energy as a Driving Force • Second law of thermodynamics • The entropy of the universe is always increasing.

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