Bellwork Thursday How much energy is required to heat a penny with a mass of 1.23 g from 15oC until it becomes red hot at 256oC? (The specific heat of copper is 0.385 J/g°C)

Unit 10 Ch 17 Part 3

Calorimetry is the measurement of heat change for chemical and physical processes. heat released by system = heat absorbed by surroundings Calorimeter- insulated device used to measure heat change in a chemical or physical process.

Coffee Cup Calorimeter

Another type of calorimeter is a bomb calorimeter Another type of calorimeter is a bomb calorimeter. In a bomb calorimeter, the heat is measured when a substance is burned. Food Calories can be determined in this way.

Bomb calorimeter

Ex. A 25 g sample of a metal at 75 Ex. A 25 g sample of a metal at 75.0oC is placed in a calorimeter containing 45 g of H2O at 23.0oC. The temperature stopped changing at 29.4oC. What is the specific heat of the metal? Find q = mC T for the water Find q = mC T for the metal substitute into q water absorbed = q metal releases Solve

Ex. A 25 g sample of a metal at 75 Ex. A 25 g sample of a metal at 75.0oC is placed in a calorimeter containing 45 g of H2O at 23.0oC. The temperature stopped changing at 29.4oC. What is the specific heat of the metal? q = mC T Twater = 29.4-23.0 = absorbed 6.4oC Tmetal = 29.4-75.0 = released 45.6oC qwater = 45g(4.18J/goC)6.4oC = 1203.84J qwater = - qmetal 1203.84J = 25g(Cmetal)45.6oC Cmetal = 1.1 J/goC

A 25g sample of a metal at 100.0 ºC is placed in a calorimeter containing 25g of H2O at 20 ºC. The temperature stopped changing at 29.4 ºC. What is the specific heat of the metal? T water = 29.4 – 20 = absorbed 9.4OC T metal = 29.4 – 100.0 = released 70.6 Solve q water q water = (25g)(4.18 J/goC)(9.4oC) = 982.3 J q water = q metal so q metal = 982.3J Solve for C in the q metal equation q = mC T 982.3 J = (25 g)Cmetal ( 70.6oC) 982.3 = 1765 Cmetal C = 0.5565439 = 0.56 J/goC

Bellwork Friday A 4.92g piece of metal is heated to 108.0°C and dropped into a calorimeter containing 60.0g of water. The water in the calorimeter is 41.0°C. The metal and water both come to a temperature of 99.0°C. What is the specific heat of the metal?

Bellwork Monday A 65.0g piece of metal is heated to 78.0°C and dropped into a calorimeter containing 100.0g of water. The water in the calorimeter is 21.0°C. The metal and water both end at a temperature of 59.0°C. What is the specific heat of the metal?

Enthalpy (H)- the amount of heat in a system at a given temperature Enthalpy change:  H = q = m C  T

Exothermic reactions have -  H Endothermic reactions have +  H

Thermochemical equations include heat changes Thermochemical equations include heat changes. Physical states must be included. CH4(g) + 2O2(g) CO2(g) + 2H2O(g) + 890 kJ  H = - 890 kJ (energy is released) exothermic 2H2O + 241.8 kJ  2H2(g) + O2(g)  H = + 241.8 kJ (energy is absorbed) endothermic (energy required)

EXAMPLE CH4(g) + 2O2(g)  CO2 + 2H2O + 890kj Exothermic – energy is a product Endothermic – energy is a reactant ∆H is also called the heat of reaction

Exothermic - energy is a product Endothermic - energy is a reactant  H is also called the heat of reaction.

Heat in Changes of State The specific heat capacity of water is 4 Heat in Changes of State The specific heat capacity of water is 4.18 J/goC or 1.00 cal/goC The specific heat ice is 2.0 J/goC and the specific heat of steam is 2.1 J/goC. This value is 0.5 cal/goC.

Notice that these have the same value, but are for opposite processes. Molar Heat of Fusion- heat required to melt one mole of a solid (6.01 kJ/mol or 334 J/g for water) Notice that these have the same value, but are for opposite processes. q = mHf Molar Heat of Solidification- heat released as 1 mole of liquid freezes. (6.01 kJ/mol or 334 J/g for water)

Notice that these have the same value, but are for opposite processes. Molar Heat of Vaporization-heat required to vaporize 1 mole of a liquid. (40.7 kJ/mol or 2260 J/g for water) Notice that these have the same value, but are for opposite processes. q = mHv Molar Heat of Condensation-heat released as 1 mole of a gas condenses to a liquid. (40.7 kJ/mol or 2260 J/g for water)

Temperature is constant during a phase change! To find the energy released in a phase change, use… q = moles or grams x heat of phase change Temperature is constant during a phase change!

Heat of vaporization and heat of condensation. They are equal amounts! Heat of fusion and heat of solidification. They are equal amounts!

Bellwork Wednesday Summary 1st Determine if the following are endothermic or exothermic. H = -226.55 kJ/mol H = -6.89 kJ/mol H = +588.457 kJ/mol H = +0.2275 kJ/mol