1. Thermochemical equations express the amount of heat released or absorbed by chemical reactions. Section 3: Thermochemical Equations K What I Know W What I Want to Find Out L What I Learned

2. 11(C) Use thermochemical equations to calculate energy changes that occur in chemical reactions and classify reactions as exothermic or endothermic. 8(A) Define and use the concept of a mole. 11(B) Understand the law of conservation of energy and the processes of heat transfer. 2(H)Organize, analyze, evaluate, make inferences, and predict trends from data. Thermochemical Equations Copyright © McGraw-Hill Education

3. Essential Questions How are thermochemical equations for chemical reactions and other processes written? How is energy lost or gained during changes of state? How is the heat that is absorbed or released in a chemical reaction calculated? Thermochemical Equations Copyright © McGraw-Hill Education

4. Review combustion reaction Thermochemical Equations Copyright © McGraw-Hill Education Vocabulary New thermochemical equation enthalpy (heat) of combustion molar enthalpy (heat) of vaporization molar enthalpy (heat) of fusion

5. Thermochemical Equations Copyright © McGraw-Hill Education Writing Thermochemical Equations A thermochemical equation is a balanced chemical equation that includes the physical states of all reactants and products, and energy change. The enthalpy (heat) of combustion of a substance is the enthalpy change for the complete burning of one mole of the substance.

6. Thermochemical Equations Copyright © McGraw-Hill Education Changes of State Molar enthalpy (heat) of vaporization refers to the heat required to vaporize one mole of a liquid substance. Molar enthalpy (heat) of fusion is the amount of heat required to melt one mole of a solid substance.

7. Thermochemical Equations Copyright © McGraw-Hill Education Changes of State

8. Thermochemical Equations Copyright © McGraw-Hill Education THE ENERGY RELEASED IN A REACTION Use with Example Problem 4. Problem A bomb calorimeter is useful for measuring the energy released in combustion reactions. The reaction is carried out in a constant-volume bomb with a high pressure of oxygen. How much heat is evolved when 54.0 g glucose (C 6 H 12 O 6 ) is burned according to this equation? C 6 H 12 O 6 (s) + 6O 2 (g)→6CO 2 (g)+6H 2 O(l) ΔH comb = -2808 kJ Response ANALYZE THE PROBLEM You are given a mass of glucose, the equation for the combustion of glucose, and ΔH comb. You must convert grams of glucose to moles of glucose. Because the molar mass of glucose is more than three times the mass of glucose burned, you can predict that the energy evolved will be less than one-third ΔH comb. KNOWN mass of glucose = 54.0 g C 6 H 12 O 6 ΔH comb = -2808 kJ UNKNOWN q = ? kJ

9. Thermochemical Equations Copyright © McGraw-Hill Education THE ENERGY RELEASED IN A REACTION EVALUATE THE ANSWER All values in the calculation have at least three significant figures, so the answer is correctly stated with three digits. As predicted, the released energy is less than one-third ΔH comb.

10. Thermochemical Equations Copyright © McGraw-Hill Education Combustion Reactions Combustion is the reaction of a fuel with oxygen. Food is the fuel in combustion reactions in biological systems.

11. Thermochemical Equations Copyright © McGraw-Hill Education Review Essential Questions How are thermochemical equations for chemical reactions and other processes written? How is energy lost or gained during changes of state? How is the heat that is absorbed or released in a chemical reaction calculated? Vocabulary thermochemical equation enthalpy (heat) of combustion molar enthalpy (heat) of fusion molar enthalpy (heat) of vaporization