Calorimetry Practice March 5th, 2018 Help Session.

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Presentation transcript:

Calorimetry Practice March 5th, 2018 Help Session

Intro What are 4 important formulas that are used for solving calorimetry problems?

Intro What are 4 important formulas that are used for solving calorimetry problems? qrxn = -qsolution q = mc∆T q = c∆T ∆H = q/n

Intro How do we determine the sign for ∆H?

Intro How do we determine the sign for ∆H (+ or -) ? The sign for ∆H depends on whether the reaction was endothermic + or exothermic - .

Problem #1 What is the specific heat of aluminum if the temperature of a 28.4 gram sample is increased by 8.1 C when 207 J of heat is added?

Problem #1 What is the specific heat of aluminum if the temperature of a 28.4 gram sample is increased by 8.1 C when 207 J of heat is added? c = 0.90 J/g*C

Problem #2 How much heat must be added to a 8.21 gram sample of gold to increase its temperature by 6.2 C? The specific heat of gold is 0.13 J/g*C.

Problem #2 How much heat must be added to a 8.21 gram sample of gold to increase its temperature by 6.2 C? The specific heat of gold is 0.13 J/g*C. q = 6.6 J

Problem #3 If 40.5 J of heat is added to a 15.4 gram sample of silver, what will the change in temperature be? The specific heat of silver is 0.235 J/g*C.

Problem #3 If 40.5 J of heat is added to a 15.4 gram sample of silver, what will the change in temperature be? The specific heat of silver is 0.235 J/g*C. ∆T = 11.2 C

Problem #4 A 2.50 gram sample of zinc is heated, then placed in a calorimeter containing 65.0 grams of water. Temperature of water increases from 20.00 C to 22.50 C. The specific heat of zinc is 0.390 J/g*C. What was the initial temperature of the zinc metal sample? (final temperatures of zinc and the water are the same)

Problem #4 A 2.50 gram sample of zinc is heated, then placed in a calorimeter containing 65.0 grams of water. Temperature of water increases from 20.00 C to 22.50 C. The specific heat of zinc is 0.390 J/g*C. What was the initial temperature of the zinc metal sample? (final temperatures of zinc and the water are the same) Ti = 720 C

Problem #5 When 0.113 grams of benzene, C6H6, burns in excess oxygen in a calibrated constant- pressure calorimeter with a heat capacity of 551 J/C, the temperature of the calorimeter rises by 8.60 C. Calculate the reaction enthalpy for the combustion of benzene (which yields carbon dioxide vapor and liquid water). (molar mass of benzene is 78.11 g/mole)

Problem #5 When 0.113 grams of benzene, C6H6, burns in excess oxygen in a calibrated constant- pressure calorimeter with a heat capacity of 551 J/C, the temperature of the calorimeter rises by 8.60 C. Calculate the reaction enthalpy for the combustion of benzene (which yields carbon dioxide vapor and liquid water). ∆ H = -3.27x103 kJ/mole

Problem #6 The value of ∆H for the reaction below is +128.1 kJ CH3OH (l)  CO (g) + 2H2 (g) How many kJ of heat are consumed when 5.10 grams of H2 (g) is formed as shown in the equation? (molar mass of H2 is 2.02 g/mole)

Problem #6 The value of ∆H for the reaction below is +128.1 kJ CH3OH (l)  CO (g) + 2H2 (g) How many kJ of heat are consumed when 5.10 grams of H2 (g) is formed as shown in the equation? ∆H = 162 kJ

Problem #7 The value of ∆H for the reaction below is +128.1 kJ CH3OH (l)  CO (g) + 2H2 (g) How many kJ of heat are consumed when 5.10 grams of CO (g) is formed as shown in the equation? (molar mass of CO is 28.01 g/mole) *remember to use mol ratio*

Problem #7 The value of ∆H for the reaction below is +128.1 kJ CH3OH (l)  CO (g) + 2H2 (g) How many kJ of heat are consumed when 5.10 grams of CO (g) is formed as shown in the equation? ∆H = 23.3 kJ