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CHEMISTRY 122

CHEMISTRY 122. HEAT OF SOLUTION. HEAT OF SOLUTION (∆H soln ). During the formation of a solution, heat is either released or absorbed The enthalpy change by dissolution of one mole of substance is the molar heat of solution Remember, a reaction can be either exothermic or endothermic.

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CHEMISTRY 122

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  1. CHEMISTRY 122 HEAT OF SOLUTION

  2. HEAT OF SOLUTION (∆Hsoln) • During the formation of a solution, heat is either released or absorbed • The enthalpy change by dissolution of one mole of substance is the molar heat of solution • Remember, a reaction can be either exothermic or endothermic.

  3. Exothermic Reactions • The heat of solution is written as a negative number to indicate that heat is being released from the system. • In the case of examples given in the textbook, both reactions are the result of heat being released from a heat pack once the substance comes into contact with water.

  4. Endothermic Reactions • The heat of reaction is positive. This indicates heat being absorbed by the system from the surroundings. • In the example given in the textbook, a cold pack, when activated by a chemical reaction with water, becomes extremely cold. Heat is moving from the surroundings to the system.

  5. Figure 17.11 • Is the process that occurs in the cold pack endothermic or exothermic? How do you know? • In which direction is the heat flowing? • Is the process in a hot pack endothermic or exothermic? How do you know? • In which direction is heat flowing?

  6. For tomorrow… • Answer the following questions: • How many kilojoules of heat are released when 25.0g of NaOH are dissolved in water? • Sketch a heating curve for 1 mole of ice being heated from -10°C to 110°C. Write a brief explanation of the graph. Calculate how much energy would be required to change 54.0g of ice at -10°C to water vapour at 110°C. • Questions 27 – 31, page 526

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