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Ch 16 Reaction Energy

Ch 16 Reaction Energy. Standard: 7.d. Students know how to solve problems involving heat flow an temperature changes, using known values of specific heat. Objective: We will define heat, give its units, and perform specific-heat calculations. Thermochemistry.

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Ch 16 Reaction Energy

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  1. Ch 16Reaction Energy

  2. Standard: • 7.d. Students know how to solve problems involving heat flow an temperature changes, using known values of specific heat. • Objective: • We will define heat, give its units, and perform specific-heat calculations.

  3. Thermochemistry • Thermochemistry: the study of the transfer of energy as heat that occurs during chemical reactions and changes in state. • Heat: q, is energy transferred from one object to another because of a temperature difference between them. • Heat always flows from a warmer object to a cooler object and will continue to flow until they are in equilibrium.

  4. Endothermic Process: one that absorbs heat from the surroundings (+q). • Exothermic Process: one that releases heat to it’s surroundings (-q). • Calorimeter: the insulated device used to measure the absorption or release of heat in chemical or physical processes.

  5. Specific Heat • Heat flow is measure in joules (J). • One joule of heat raises the temperature of 1g of pure water 0.2390°C • Specific Heat: the amount of heat needed to increase the temp of 1 g of the substance 1°C. • The specific heat is the heat capacity of an object divided by its mass in grams.

  6. Calculating Specific Heat (C) • Divide the heat input, q (Joules) by the temperature change, ΔT (°C) times the mass of the substance, m (g). C = q = heat m x ΔTmass x change in temp

  7. Example • The temperature of a 95.4 g piece of copper increases from 25.0°C to 48.0°C when the copper absorbs 849 J of heat. What is the specific heat, C, of copper? q = 849 J m = 95.4g ΔT = (48.0°C -25.0°C)=23.0°C C = q = 849 J m x ΔT 95.4 g x 23.0°C C = 0.387 J/(g x °C)

  8. Example 2 • How much heat, q, is required to raise the temperature of 400.0 g of silver 45°C? The specific heat of silver is 0.24 J/(g x °C). ΔT = 45°C m = 400.0 g C= 0.24 J/(g x °C) q = C x m x ΔT q = 0.24 J/(g x °C) x 400.0 g x 45°C q = 4320 J

  9. Homework Notes • Table 1 is on page 533. • Kelvin and Celsius are interchangeable because they are on the same scale. • cp is the same as C • #7 solve for q • #8 solve for ΔT, add that to 20°C and then convert to Kelvin. • ΔT = q /(C x m) • #9 solve for C • #10 change mol to g and solve for C

  10. Chapter 17Reaction Kinetics

  11. Ch 17.1 Reaction Kinetics

  12. Standard: • 8.a. Students know the rate of reaction is the decrease in concentration of reactants or the increase in concentration of products with time. • Objective: • We will use the collision theory to interpret chemical reactions and define activated complex. We will draw energy diagrams.

  13. Collision Theory • Collision Theory: atoms, ions, and molecules can react to form products when they collide with each other, provided that the colliding particles have enough kinetic energy. • Think about two balls of clay. If you throw them together gently, they won’t stick together, but if there is enough energy, they will stick together.

  14. Rate: a measure of the speed of any change that occurs within an interval of time. • In chemistry, the rate of chemical change or the reaction rate is usually expressed as the amount of reactant changing per unit time. • Activation Energy: the minimum energy that colliding particles must have in order to react.

  15. Activated Complex: an unstable arrangement of atoms that forms momentarily at the peak of the activation-energy barrier. • This is also called the Transition Rate.

  16. Sample Problem A page 566andPractice Problem 2page 567

  17. Ch 17.2

  18. Standard: • 8.b. Students know how reaction rates depend on such factors as concentration, temperature and pressure. • 8.c. Students know the role a catalyst plays in increasing the reaction rate. • Objective: • We will discuss the factors that influence reaction rate and define a catalyst.

  19. Factors Affecting Reaction Rates • The rate of a chemical reaction depends upon temperature, concentration, particle size, and the use of a catalyst. TEMPERATURE • Raising the temperature speeds up the reaction and lowering the temperature slows down the reaction.

  20. CONCENTRATION • The higher the concentration, the more likely collisions will take place, which increases the reaction rate. PARTICLE SIZE • The smaller the particle size, the more surface area, which increases the reaction rate.

  21. CATALYSTS • Adding a catalyst will increase the rate of reaction, in some cases, better than increasing the temperature. • Inhibitor: a substance that interferes with the action of a catalyst. • These will slow down or even stop a reaction

  22. Nature of Reactants • The nature of the reactants involved in the chemical reaction also play a part. But just remember the first four.

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