Exam 6: Thermochemistry

According to the following reaction,how much energy is evolved during the reaction of 2.50 L B₂H₆ and 5.65 L Cl₂ (both gases are initially at STP)? The molar mass of B₂H₆ is 27.67 g $\mathrm { mol } ^ { - 1 }$ . B₂H₆(g)+ 6Cl₂(g)? 2BCl₃(g)+ 6HCl(g) D_rH° = -1396 kJ

Calculate the internal energy change,Δ_rU,for the combustion of 9.467 g of L-alanine (C₃H₇NO₂,molar mass = 89.094 g mol^-1)if the combustion inside a bomb calorimeter,C_cal = 7.83 kJ °C^-1,causes a temperature change from 24.7 °C to 46.1 °C.

When 50.0 mL of 0.400 mol L^-1 Ca(NO₃)₂ is added to 50.0 mL of 0.800 mol L^-1 NaF,CaF₂ precipitates,as shown in the net ionic equation below.The initial temperature of both solutions is 24.0 °C.Assuming that the reaction goes to completion,and that the resulting solution has a mass of 100.00 g and a specific heat of 4.18 J $g ^ { - 1 }$ ${ } ^ { \circ } \mathrm { C } ^ { - 1 }$ ,calculate the final temperature of the solution. Ca²⁺(aq)+ 2F^-(aq)? CaF₂(s) $\Delta _ { \mathrm { r } }$ H = -11.5 kJ

For a process at constant pressure,62,000 calories of heat are absorbed.This quantity of heat is equivalent to

Calculate the amount (mass)of acetic acid (C₂H₄O₂,molar mass = 60.052 g mol^-1)that causes a bomb calorimeter with a heat capacity of 8.43 kJ °C^-1 to have a temperature increase from 24.5 °C to 36.8 °C.The D_rU for the combustion of acetic acid is -874.2 kJ mol^-1.

At 1.0133 bar,the heat of sublimation of gallium is 277 kJ $\mathrm { mol } ^ { - 1 }$ and the heat of vaporization is 271 kJ $\mathrm { mol } ^ { - 1 }$ .To the correct number of significant figures,how much heat is required to melt 5.50 mol of gallium at 1.0133 bar?

Use the _DfH° and _DrH° information provided to calculate _DfH° for SO₃(g): 2(g)+(g)\rightarrow2(g)=-198 (g)-297

In the presence of excess oxygen,methane gas burns in a constant pressure system to yield carbon dioxide and water: $\mathrm { CH } _ { 4 }$ (g)+ $2 \mathrm { O } _ { 2 }$ (g)? $\mathrm { CO } _ { 2 }$ (g)+ $2 \mathrm { H } _ { 2 }$ O (l) $\Delta _ { \mathrm { r } }$ H = -890.0 kJ Calculate the value of q (kJ)in this exothermic reaction when 1.90 g of methane is combusted at constant pressure.

According to the following thermochemical equation,what mass of HF (in g)must react to produce 345 kJ of energy? Assume excess SiO₂. SiO₂(s)+ 4HF(g)→ SiF₄(g)+ 2H₂O(l) D_rH° = -184 kJ

Where does the energy absorbed during an endothermic reaction go?

Calculate the amount of heat (in kJ)required to raise the temperature of a 79.0 g sample of ethanol from 298.0 K to 385.0 K.The specific heat capacity of ethanol is 2.42 J g^-1 °C^-1.

Describe the energy changes that occur when a book is held 1 m off the floor and then dropped.

Calculate the change in internal energy (ΔU)for a system that is giving off 25.0 kJ of heat and is changing from 12.00 L to 6.00 L in volume at 1.50 bar.(Remember that 100 J = 1 L bar)

Calculate the enthalpy of solution for the dissolution of lithium iodide,LiI,molar mass = 133.85 g mol^-1.When 1.49 g of LiI is dissolved in a coffee cup calorimeter containing 75.0 mL of water the temperature increased from 23.5 °C to 25.7 °C.The specific heat of water is 4.184 J g^-1 °C^-1,and assume the density of the solution is 1.00 g mL^-1.

Which of the following is in a non-standard state?

A chemist wishes to calibrate a bomb calorimeter,so she combusts 5.58 g of 4-pentenoic acid,Δ_combustionU = -26.77 kJ g^-1,which causes a temperature change from 23.4 °C to 38.9 °C.What should the chemist report for the value of C_cal?

How much energy is evolved during the reaction of 48.7 g of Al according to the reaction below? Assume that there is excess Fe₂O₃. Fe₂O₃(s)+ 2Al(s)→ Al₂O₃(s)+ 2Fe(s) D_rH° = -852 kJ

Identify the greatest source of energy worldwide.

Use the information provided to determine _DrH° for the following reaction: (g)+4(g)\rightarrow(g)+4(g) =? (g) -75 (g) -96 (g)-92

9.26 g of an unknown solid is dissolved in a coffee cup calorimeter that contains 62.0 mL of water.The measured temperature increased from 23.4 °C to 24.7 °C.The specific heat of water is 4.184 J g^-1 °C^-1,and assume the density of the solution is 1.00 g mL^-1.Calculate the molecular weight of the unknown solid if the $D _ { \mathrm { r } }$ H was determined to be -2.51 kJ mol^-1 via another experiment.