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Energy and Heat Transfer in Chemistry

Learn about the different forms of energy and how they can be transferred in chemistry. Understand concepts such as potential energy, kinetic energy, heat, and temperature. Explore calorimetry and thermochemical equations.

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Energy and Heat Transfer in Chemistry

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  1. Energy Flashcards(unit 3)

  2. ENERGY The ability to do work

  3. Potential Energy Energy of position. Stored energy.

  4. Kinetic Energy Energy of motion Depends on how heavy & how fast

  5. Radiant Energy Electromagnetic Energy

  6. Units of Energy Joules – SI system Calories - English

  7. Energy in Chemistry Chemical Potential Energy – stored in chemical bonds Heat – form of energy that flows between objects at different temperatures. Heat – form of energy associated with the random motion of atoms & molecules. Hot atoms move fast!

  8. The potential energy a molecule possesses by virtue of its structure and composition. Chemical Potential Energy

  9. Direction of heat flow Hot to Cold

  10. Q Symbol for heat energy

  11. Temperature A measure of the avg. kinetic energy of the particles of a system. Temperature is NOT energy.

  12. Differences between heat & temperature? They have different units! Heat energy depends on how much stuff! Temperature does not.

  13. As the temperature , the avg. kinetic energy … Increases!

  14. As the temperature , the avg. kinetic energy … Decreases!

  15. When the temperature is constant, the avg. kinetic energy … is constant!

  16. How is Kinetic Energy transferred between particles? In collisions!

  17. a) b) c) d) Graph a Which graph best shows the relationship between Kelvin temperature & average KE?

  18. Law of Conservation of Energy Total energy is conserved. Energy before = Energy after Energy lost = Energy gained Energy can be converted from 1 form to another. Energy can flow between the system and the environment.

  19. Environment System Energy Energy of Universe is conserved Universe Energy can move between the system and the environment. Environment

  20. Environment System Energy EXO - energy leaves system (exits). Temperature of environment  Temperature of system  System has a net loss in energy! H is –’ve.

  21. Exothermic Process System releases energy (heat) to environment.

  22. Environment System Energy Endo - Energy enters system (entrance) Temperature of environment . Temperature of system . System has a net gain in energy! H is +’ve.

  23. Endothermic Process System absorbs energy (heat) from environment

  24. Quantity of heat transferred depends on … Q = mCT Temperature change Mass of substance Specific Heat of substance

  25. Specific Heat Amount of energy required to raise the temperature of one gram of a substance by 1C. Different for every substance. CH2O = 4.18 J/g (Table B)

  26. Symbol for specific heat C (upper case) for NYS Regents s (lower case) for almost everyone else.

  27. Q = mCT Equation used to calculate energy change when a pure substance in one phase is heated or cooled.

  28. Calorimetry: the process of measuring the heat absorbed or released during a chemical or physical change. Relies on the Law of Conservation of Energy Coffee Cup calorimeter or Constant Pressure Calorimeter

  29. Calculating Heat Transferred Q = mCT • Q = amount of heat transferred • m = mass of substance • C = specific heat capacity of the substance (Table B). • T = temperature change = Tfinal – Tinitial

  30. Calculating energy changes in H2O Q C m T

  31. Dissolving EXOTHERMIC! • When 10 g NaOH dissolves, the temperature of the H2O increases. Add 100 g H2O Styrofoam Cup Close together. Not interacting with H2O. Pulled apart & interacting with H2O.

  32. Calorimetry • The H2O is the environment. • The NaOH in the water is the system. Styrofoam Cup Initial temperature of water = 22C Temperature = 30C

  33. Exothermic In a calorimetry exp’t, H2O is the environment. The system is the stuff in the water. If the temperature of the H2O , the process was ______________. exothermic

  34. Endothermic In a calorimetry exp’t, H2O is the environment. The system is the stuff in the water. If the temperature of the H2O , the process was ______________. endothermic

  35. Energy and Stability If energy is high, stability is low. If enrgy is low, stability is high.

  36. Energy Changes at Phase Changes Gas Going Up the ladder = Endothermic Process Net gain in energy. Going Down the ladder = Exothermic Process Net loss in energy. Potential Energy of System Liquid As a substance moves up the ladder, the distance between its molecules increases. Molecules are ALWAYS attracted to one another. Solid

  37. How do we assess changes in average kinetic energy? By looking at changes in temperature!

  38. How do we assess changes in potential energy? By looking at changes in phase!

  39. Fill in the name and energy change (endo or exo) Melting or fusion Endothermic Sublimation Endothermic Evaporation / Boiling Endothermic Freezing Exothermic Condensation Exothermic Exothermic Deposition

  40. Freezing point Solid-Liquid Equilibrium Temperature Melting Point

  41. Liquid-Gas Equilibrium Temperature Boiling Point

  42. Thermochemical Equation 2NH4Cl(s) + Ba(OH)28H2O + heat  2NH3(g) + BaCl2(s) + 10H2O(l) Shows chemical information andHeat Flow information

  43. 3H2(g) + N2(g)  2NH3(g) + Heator3H2(g) + N2(g)  2NH3(g) + 91.8 kJ Heat term is on the product side Exothermic Reaction

  44. H2(g) + I2(g) + heat  2HI(g)orH2(g) + I2(g) + 53.0 kJ 2HI(g) Heat term is on the reactant side. Endothermic Reaction.

  45. In what kind of change do the products have MORE potential energy than the reactants? The only way to get to higher PE is to absorb some energy from the environment! Endothermic! P.E. Products Reactants

  46. In what kind of change do the products have LESS potential energy than the reactants? The only way to get to lower PE is to release some energy to the environment! Exothermic! P.E. Reactants Products

  47. How do the sizes of the centigrade degree and the Kelvin compare? The Kelvin and centigrade degree are the same size! They both have 100 degrees between the freezing point of water and the boiling point of water.

  48. The temperature of a sample of a substance changes from 50C to 85C. How many Kelvin degrees does the temperature change? 50C + 273 = 323 K 85C + 273 = 358 K 358 K – 323 K = 35 K Hey! 85C - 50C = 35C When you take a difference, the number is the SAME!

  49. What kind of intermolecular forces do solids have? Strong IMF!

  50. What kind of intermolecular forces do gases have? Weak IMF!

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