Energy of Phase Changes
Explain why the standard enthalpy of vaporization values for CH4 and H2O are not the same
CH4 has LDF while H2O has H-bonds so the standard enthalpy of vaporization for water would be higher.
A 85.2 g copper bar was heated to 221.32 C and placed in a coffee cup calorimeter containing 425.0 mL of water at 22.55 C. The final temperature of the water was recorded to be 26.15 C. How much heat was gained by the water
6400 J
Using only information given in the thermochemical equation below, make a comparison between the sum of the bond enthalpies of the reactants and the sum of the bond enthalpies of the products. Explain why one value is greater than the other.
CH4 +2O2-> CO2+2H2O ΔHrxn=-802.3 kJ/mol
The value for the bond enthalpies of the products is greater than the bond enthalpies of the reactants because the reaction is exothermic, so it loses energy
Using the standard enthalpy of formation values, calculate the enthalpy of combustion ΔHcomb of one mole of ethane at 25 C.
C2H6+3.5 O2-> 2CO2 +3H2O
-1559.83 kJ/mol
Determine the value of the enthalpy change, ΔHrxn, for the reaction 2Fe2O3+3C(graphite)->4Fe+3CO2
C(graphite)+O2->CO2 ΔH=-393.5 kJ/mol
8Fe+6O2->4Fe2O3 ΔH=-3296.8 kJ/mol
467.9 kJ/mol
Explain why the temperature of a liquid remains constant while it is being boiled, although heat continues to be absorbed. Describe what happens to the heat that is absorbed.
The liquid is not increasing in temperature because the KE is not increasing. The heat that is absorbed is used to break IMF.
The specific heat capacity of copper is 0.385 J/(gK). If 353 J of heat are added to 3.6 moles of copper at 283 K, what is the final temperature of the sample of copper
287K
Use the chemical equation below and the table of average bond energies to answer the following questions. Calculate the enthalpy change ΔHrxn that occurs in the reaction.
N2+3H2->2NH3
-109 kJ/mol
Calculate the enthalpy of reaction ΔH for the formation of carbon dioxide from graphite and oxygen gas. C(graphite) + O2 ->CO2
-393.509 kJ/mol
Determine the value of the enthalpy change for the evaporation of one mole of water using the information below. H2O(l)->H2O(g)
CH4+2O2->CO2+2H2O(l) ΔH=-890.5 kJ/mol
CH4+2O2->CO2+2H2O(g) ΔH=-802.3 kJ/mol
44.1 kJ/mol
HBr is a molecular solid rather than an ionic solid, meaning it is weaker in therms of IMF.
The specific heat capacity of iron is 0.45 J/gK. Find the molar heat capacity for iron. If 1239 J of heat are added to 5.6 mole sample of Fe at 12.2 C, what is the final temperature of the sample?
25.13 J/molK, 21 C
Use the thermochemical equation for the combustion of methane and the table of average bond energies to find the average bond energy in a C-H bond.
CH4+2O2->CO2+2H2O ΔHrxn=-802.3
416.425 kJ/mol
Calculate the enthalpy change ΔH for the formation of liquid water from liquid water vapor H2O(l)->H2O(g)
44.012 kJ/mol
Determine the value of the enthalpy change for the following reaction: N2O + NO2-> 3NO
2NO->N2+O2 ΔH=-181 kJ/mol
2N2O->2N2+O2 ΔH=-163 kJ/mol
NO+1/2O2->NO2 ΔH=-57 kJ/mol
156.5 kJ/mol
How much heat is required to melt a 12.5 mol pure sample of ice at 0 C. ΔHfus=6.01 kJ/mol
75.125 kJ
How much heat is released when 24.8 g of CH4 is burned in excess oxygen gas to produce carbon dioxide and water? ΔHrxn=-802.3 kJ/mol
CH4 + 2O2-> CO2 +2H2O
-1239.55 kJ
Use the chemical equation and the table of average bond energies to answer the following questions.
C3H4+4O2->3CO2+2H2O
Calculate the enthalpy change ΔHrxn, that occurs in the reaction
-1794 kJ/mol
The standard heat of formation of B2O3 is -1263.6 kJ/mol and the standard heat of formation of liquid water is -285.8 kJ/mol. Find the standard heat of formation for one mole of B5H9.
2B5H9+12O2-> 5B2O3 + 9H2O
73.2 kJ/mol
Determine the value of the enthalpy change for the following reaction.
C2H4 + 6F2->2CF4+4HF
2C2H4->4H2+4C ΔH=-104.6 kJ
CF4->C+2F2 ΔH=680.0 kJ
H2+F2->2HF ΔH=-537 kJ
-2486.3 kJ/mol
How much heat is required to melt 12.6 g of 24-carat gold at 298 K? The melting temperature of 24-carat gold is 1063 C. The molar heat capacity of 24-carat gold is 25.6 J/molK and the heat of fusion for 24-carot gold is 12.5 kJ/mol
1698.8 J
Ammonia is produced from a reaction between hydrogen gas and nitrogen gas. ΔHrxn=-92.2 kJ/mol
-2090.48 kJ
2C2H2 + 5O2 -> 4CO2 +2H2O
Calculate the enthalpy change ΔHrxn that occurs in this reaction
-2197 kJ/mol
Using standard enthalpy of formation values. Calculate the enthalpy of combustion, ΔHcomb, for one mole of methanol at 25 C
CH3OH+1.5 O2-> CO2+2H2O
-784.5 kJ/mol
Determine the value of the enthalpy change for the following reaction
C+H2O-> CO+H2
C+O2-> CO2 ΔH=-394 kJ
2CO+O2->2CO2 ΔH=-566 kJ
2H2+O2->2H2O ΔH=-484 kJ
131 kJ/mol