Calorimetry Practice Problems

Common Core Connection Objectives Today I will be able to: Calculate the heat absorbed and released in a chemical reaction Informal assessment – monitoring student interactions and questions as they complete the practice problems Formal assessment – analyzing student work from the practice problems and exit ticket Common Core Connection Make sense of problems and persevere in solving them Reason abstractly and quantitatively

Lesson sequence Evaluate: Warm Up Directed Practice Problems Formal assessment Directed Practice Problems Informal assessment Individual Practice Problems Informal/formal assessment Evaluate: Exit Ticket

Warm Up Carbon exists in two natural forms: graphite and diamond. Each form can be combusted: C(graphite) + O2(g)  CO2(g) ∆H = -393.5 kJ C(diamond) + O2(g)  CO2(g) ∆H = -395.4 kJ Calculate ∆H of the conversion of graphite to diamond: C(graphite)  C(diamond) HW: Finish Calorimetry Problems

Objectives Today I will be able to: Calculate the heat absorbed and released in a chemical reaction

Homework Study for Thermochemistry Quiz on Wednesday, April 15

Agenda Warm Up Directed Practice Problems Individual Practice Problems Exit Ticket

Directed Practice Problems

Hess’s Law Calculate ∆H for the reaction 4 NH3 (g) + 5 O2 (g)  4 NO (g) + 6 H2O (g), from the following data. N2 (g) + O2 (g)  2 NO (g) ∆H = -180.5 kJ N2 (g) + 3 H2 (g)  2 NH3 (g)∆H = -91.8 kJ 2 H2 (g) + O2 (g)  2 H2O (g) ∆H = -483.6 kJ

Calorimetry Example 1: You put 103.0 g of aluminum in 100.0 grams of boiling water. The water temperature changes from 100.0ºC to 90.0ºC, while the aluminum temperature goes from 25.0ºC to 70.0ºC. What is the specific heat of aluminum?

Calorimetry H2O Al -(103.0g)(c)(70.0-25.0°C) (100.0g)(4.184J/g°C)(90.0-100.0°C) = -4640 g°C(c) = -4180 J c = 0.901 J/g°C

Another type… What if something dissolves in the water? What happens to the total mass??? You add them up! The whole solution increases (or decreases) in heat.

Example A chemistry student dissolves 4.51 grams of room temperature sodium hydroxide in 100.00 g of water at room temperature, 19.5°C. As the sodium hydroxide dissolves, the temperature of the solution increases to 31.7°C. Determine the heat of solution of the sodium hydroxide in J/mol.

Answer 47.3 kJ/mol

Let’s Practice Calorimetry Problems You may check Ms. Ose’s answer key as you work

Exit Ticket Based on the calorimetry data presented below, is the reaction endothermic or exothermic? Explain.