# Friday 2/28 1. If the H of a reaction = -3167 J, is the reaction endothermic or exothermic? 2. If this reaction took place in water, what would happen.

## Presentation on theme: "Friday 2/28 1. If the H of a reaction = -3167 J, is the reaction endothermic or exothermic? 2. If this reaction took place in water, what would happen."— Presentation transcript:

Friday 2/28 1. If the H of a reaction = -3167 J, is the reaction endothermic or exothermic? 2. If this reaction took place in water, what would happen to the waters temperature? How do you know this? 3. What is the equation for heat/enthalpy absorbed or released? What is the unit for heat/enthalpy? 4. What is specific heat capacity? What is the symbol? 5. What is the instrument used to measure heat change?

11.3 Heat of Fusion and Solidification: p.307 H fus = molar heat of fusion Heat absorbed by 1 mol of substance when it changes from a solid to a liquid H solid = molar heat of solidification Heat released by 1 mol of substance when it changes from a liquid to a solid H solid and H fus are opposites H 2 O (s) --> H 2 O (l) H fus = 6.01 kJ / mol H 2 O (l) --> H 2 O (s) H solid = - 6.01 kJ / mol

Heat of Vaporization and Condensation: p. 310 H vap = molar heat of vaporization Heat absorbed by 1 mol of substance when it changes from a liquid to a gas H cond = molar heat of condensation Heat released by 1 mol of substance when it changes from a gas to a liquid H vap and H cond are opposites, too! 40.7kj/mol H vap = - H cond

Heat of solution: p.312 When a solute dissolves in a solvent, an endothermic or an exothermic reaction may occur (refer to the demonstrations from last class) When a solute dissolves in a solvent, an endothermic or an exothermic reaction may occur (refer to the demonstrations from last class) Recall the examples from Monday: the sodium hydroxide RELEASED energy into the water (exothermic) and the ammonium nitrated ABSORBED energy from the water (endo) Recall the examples from Monday: the sodium hydroxide RELEASED energy into the water (exothermic) and the ammonium nitrated ABSORBED energy from the water (endo)

Values for H fus and H vap are on page 308 (Table 11.5) Ex: How much heat (in kJ) is absorbed when 63.7 g H 2 O (l) at 100. o C is converted to steam at 100. o C? Mass of water = 63.7 g H vap = ?? (check on the table!) Solve for: H = ? Is the reaction endo or exo-thermic? Reaction: H 2 O (l) + 40.7 kJ --> H 2 O (g)

Heating curve for water: p.310 How does heat supplied differ from temperature? How does heat supplied differ from temperature? How does the heat of fusion differ from the heat of vaporization? How does the heat of fusion differ from the heat of vaporization? How does this explain waters heat capacity? How does this explain waters heat capacity?

Practice problems: How many grams of ice could be melted by the addition of 0.400 KJ of heat? (assume STP) How many grams of ice could be melted by the addition of 0.400 KJ of heat? (assume STP) How many KJ of heat are absorbed when 0.46 g of C 2 H 5 Cl, bp 12.3 °C vaporizes at its boiling point? The molar heat of vaporization is 26.4 KJ/mol. How many KJ of heat are absorbed when 0.46 g of C 2 H 5 Cl, bp 12.3 °C vaporizes at its boiling point? The molar heat of vaporization is 26.4 KJ/mol. How much heat is KJ is released when 0.677 mol of sodium hydroxide are dissolved in water? How much heat is KJ is released when 0.677 mol of sodium hydroxide are dissolved in water?

Homework p 306 # 15, 16, 19; p 322 # 43, 49, 50, 51; p 313 # 26, 28; p 322 # 53ab, 54 p 306 # 15, 16, 19; p 322 # 43, 49, 50, 51; p 313 # 26, 28; p 322 # 53ab, 54

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