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Chapter 16 Reaction Energy

Chapter 16 Reaction Energy. West Valley High School General Chemistry Mr. Mata. Standard 7b. Students will know that chemical processes can either release or absorb thermal energy. Essential Question:. How is heat used to measure energy in chemical reactions?. Heat vs Temperature. Heat

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Chapter 16 Reaction Energy

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  1. Chapter 16Reaction Energy West Valley High School General Chemistry Mr. Mata

  2. Standard 7b • Students will know that chemical processes can either release or absorb thermal energy.

  3. Essential Question: • How is heat used to measure energy in chemical reactions?

  4. Heat vs Temperature • Heat • measure of energy change in a system. • Temperature • measure of the kinetic energy (movement) of the particles in a system. • Gaining or losing heat energy in a substance can change its temperature. • Exothermic • System loses energy to surroundings. • Endothermic • System gains energy from surroundings.

  5. Specific Heat Capacity • Specific Heat Capacity • measure of how a substance reacts to heat energy changes. • The symbol we use is cp. • The “p” stands for pressure (constant) while heat is added or lost. • Specific Heat • property of matter, diff substances have diff specific heats. • Specific Heat Capacity • heat energy required to raise 1 gram of pure substance 1 degree Celsius.

  6. Specific Heat Capacity • Metals have very low cp, • why metals feel cold to touch. • Water has a very highcp, • 4.184 J/g·0C • Substances with lower cp will rise in temperature faster and require less energy to do so than do substances with high cp. 1 calorie=4.184 Joules

  7. Calculating Heat Energy • Cp=Joules / (gram * degree) • Change in heat (Joules, J) • = • Change in temperature (degree, 0C) • x • Mass (mass, g) • x • Specific Heat Capacity

  8. Enthalpy, ΔH • Enthalpy • heat energytransferred for a specific change to take place. • We specify enthalpy with ΔH. • “Δ” means “change”. • Exothermic reaction • negative enthalpy (-ΔH) • Endothermic reaction • Positive enthalpy (+ΔH).

  9. Devices to Measure ΔHcomb The Calorimeter (shown) Heat energy transferred from a reaction inside the calorimeter to the water in the calorimeter. The temperature change of the water is observed. A Bomb Calorimeter uses a chamber of pure oxygen to measure heats of combustion to the 1/1000 of a joule.

  10. Reaction Enthalpy • If ΔH is negative, reaction is exothermic. • C6H12O6 + 6O26CO2 + 6H20 + 2870kJ • ΔHrxn = -2870 kJ/mol • If ΔH is positive, reaction is endothermic. • 2H2O + 571.6kJ 2H2 + O2 • ΔHrxn = +571.6 kJ/mol energy

  11. Chapter 16 SUTW Prompt • Describe the differences between exothermic and endothermic in a chemical reaction. • Complete a 8 -10 sentence paragraph using the SUTW paragraph format. Hilight using green, yellow, and pink. • Due Date: Monday, March 12th, 2018 (start of class).

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