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Understanding Exothermic and Endothermic Reactions in Chemistry

Explore the concepts of exothermic and endothermic reactions in chemistry, including heat transfer, energy transformations, and enthalpy calculations. Learn how to differentiate between these reactions and analyze heat changes during chemical processes. Practice solving enthalpy problems to enhance your understanding of reaction energy. Highlight key principles of thermochemistry and energy transformations in this comprehensive guide.

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Understanding Exothermic and Endothermic Reactions in Chemistry

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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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