1 / 10

Chapter 16

Chapter 16. Reaction Energy. Thermochemistry. The study of the transfers of energy as heat that accompany chemical reactions and physical changes. Heat and Temperature. Calorimeter – measures the energy absorbed or released as heat in a chemical or physical change.

winfred-smith
Download Presentation

Chapter 16

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chapter 16 Reaction Energy

  2. Thermochemistry • The study of the transfers of energy as heat that accompany chemical reactions and physical changes.

  3. Heat and Temperature • Calorimeter – measures the energy absorbed or released as heat in a chemical or physical change. • Temperature – measures the average kinetic energy of the particles in a sample of matter. • Greater the kinetic energy of the particles in a sample, the higher the temperature is and the hotter it feels. • Joule – unit of heat as well as all other forms of energy. • Heat – energy transferred between samples of matter. (moves spontaneously from matter at a high temperature to matter of a lower temperature.

  4. Specific Heat – quantity of heat required to raise the temperature of one gram of a substance by one degree Celsius. • The quantity of energy transferred as heat during a temperature change depends on the nature of the material changing temperature, the mass of the material changing temperature, and the size of the temperature change. • The difference depends on the metal’s differing capacities for absorbing this energy. • A quantity called specific heat can be used to compare heat absorption capacities for different materials. • cp = q / m x delta T (Specific heat at a given pressure) • q = cp x m x delta T (Quantity of energy gained or lost with a change in temperature.)

  5. Enthalpy of Reaction pg534 • The energy absorbed as heat during a chemical reaction at constant pressure is represented by delta H. • Enthalpy Change – amount of energy absorbed by a system as heat during a process at constant pressure. • Delta H = Hproducts – Hreactants • Enthaply of Reaction is the quantity of energy transferred as heat during a chemical reaction. (Heat of reaction)

  6. Thermochemical Equation pg535 • An equation that includes the quantity of energy released or absorbed as heat during the reaction. • Examples: • 2H2(g) + O2(g) 2H2O(g) + 483.6 kJ (exothermic) • Enthaply change is negative = energy released • Delta H = - 483.6 kJ • 2H2O(g) + 483.6 kJ  2H2(g) + O2(g) (endothermic) • Enthaply change is positive = energy absorbed • Delta H = + 483.6 kJ • See rules: pg 537

  7. Enthalpy of Formation pg537 • Formation of a compound from its elements in their standard form. • The molar enthalpy of formation is the enthalpy change that occurs when one mole of a compound is formed from its elements in their standard state at 25oC and 1 atm. • Delta Hof • Appendix Table A-14 pg 862

  8. Enthalpy of Reaction Calculations pg 539 • Pg.552 Problem 15a • -1207.6 -634.9 -393.5 • CaCO3(s) -------> CaO(s) + CO2(g) • -1207.6 0 0 0 • CaCO3 ------- Ca + C + 3/2O2 Hf0 = +1207.6 kJ • 0 0 -634.9 • Ca + 1/2O2 - CaO Hf0 = -634.9 kJ • 0 0 -393.5 • C + O2 --- CO2 Hf0 = -393.5 kJ • __________________________________________ • CaCO3(s) ------ CaO(s) + CO2(g) H = +179.2 kJ • (endothermic and unstable) • Hint: Hf0 = heat of formation • + = endothermic • - = exothermic • More negative the enthalpy of formation is, the more stable a compound is.

  9. Driving Force of Reactions • Two factors that determines if a reaction will occur spontaneously (Define spontaneously?): • Change in energy • Randomness of the particles • Tendencies (Enthalpy + Reaction): • Exothermic: energy released, less energy in products, products resist to change, more stable. Natural direction that leads to a lower energy state. • Endothermic: energy absorbed, not spontaneous, products are at higher potential energy, and are less stable. Need outside influence (heat etc..) to proceed. • Tendencies (Entropy + Reaction): • Increase [(+) delta S] in randomness (entropy) reaction is spontaneous.

  10. Free Energy • Processes in nature are driven in two directions: toward least enthalpy and toward largest entropy. When these two oppose each other, the dominant factor determines the direction of change. This combined enthalpy-entropy function is called the free energy, G, of the system; it is also called Gibbs free energy. • Natural processes proceed in the direction that lowers the free energy of a system. • Only the change in free energy can be measured. • Delta G0 = delta H0 – T delta S0 • The reaction will be spontaneous if you have a negative delta G. • The reaction will not be spontaneous if you have a positive delta G. • Another option: See table 2 pg 549

More Related