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Chapter 16 Reaction Energy

Chapter 16 Reaction Energy. West Valley High School General Chemistry Mr. Mata. ENERGY TRANSFORMATIONS. Thermochemistry - Heat gain/loss in chemical changes Physical change Ex: boiling, evaporation Chemical change Ex: combustion, combination Energy-

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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. ENERGY TRANSFORMATIONS • Thermochemistry- Heat gain/loss in chemical changes • Physical change • Ex: boiling, evaporation • Chemical change • Ex: combustion, combination • Energy- • Ability to do work or supply heat. • Energy can not be observed, only detected because of its effects.

  3. Chemical potential energy-energy stored in chemical bonds. • When chemical bonds are broken and rearranged, energy is released or absorbed. • H-heat energy that is transferred from one object to another .(book uses q, not H) • ∆H is the change in heat energy. • Heat always flows from the warmer object to the cooler one.

  4. ENDOTHERMIC AND EXOTHERMIC PROCESS • To study heat, must define the system and surroundings. • Together the system and the surroundings constitute the universe. • Law of Conservation of Energy • Energy lost = energy gained. • Energy is neither created nor destroyed.

  5. Enthalpy  H = m x Cp x T • ( H = Q = q = heat = enthalpy) • m = mass • Cp = specific heat capacity (table) • T = T(final) – T (initial) 

  6. Enthalpy Problem #1 When 100 mL of water at 26 C is mixed in a calorimeter, the temperature of the solution decreases to 22 C. How much heat (in Joules) was released in the reaction? Known: Cp H2O = 4.18 J/g * C unknown:q = ? J T = Tf– Ti = 22 C – 26 C = - 4 C m = 100 mL H2O x 1 g H2O = 100 g H2O 1 mL H2O q = m x Cp x T = (100 g) (4.18 J/g *C) (- 4 C) = - 1672 J Endothermic or Exothermic reaction??? EXOTHERMIC ( - q value) 

  7. Enthalpy Problem #2 A small pebble is heated and placed in a foam cup calorimeter containing 25 mL of water at 25 C. The water reaches a maximum temperature of 26.4 C. How many joules of heat were released by the pebble? Known: m H2O = 25 g T = Tf– Ti = 26.4 C – 25 C = 1.4 C Cp H2O = 4.18 J/g * C unknown = q = ? J q = m x Cp x T = (25 g) (4.18 J/g *C) (1.4 C) = q = 146.3 J Exothermic or Endothermic reaction??? ENDOTHERMIC ( + q value) 

  8. Chapter 16 SUTC 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: Tomorrow (start of class).

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