1) The molar heat capacity of Al(s) is 24.2 J/K•mol. Calculate the molar enthalpy change when Al(s) is cooled from 128.5°C to 22.6°C.

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1) The molar heat capacity of Al(s) is 24.2 J/K•mol. Calculate the molar enthalpy change when Al(s) is cooled from 128.5°C to 22.6°C.
To dete
tive enthalpy changes are exothermic.
mole. The enthalpy value is negative, which indicates a cooling process.
The calculation shows the molar enthalpy change has units of joules per
lpy change, use the equation AH = CAT.
final value,
initial valu-
Calculate.
than the fi
AH = CAT
(24.2 J/K•mol)(-15 K) = -360 J/mol
Verify your results.
PRACTICE
The molar heat capacity of Al(s) is 24.2 J/K•mol. Calculate the molar
onthalpy change when Al(s) is cooled from 128.5°C to 22.6°C.
Lead has a molar heat capacity of 26.4 J/K•mol. What molar enthalpy
PRO
SO
S
change occurs when lead is cooled from 302°C to 275°C?
3 Calculate the molar enthalpy change when mercury is cooled 10 K.
The molar heat capacity of mercury is 27.8 J/K•mol.
Enthalpy Changes of Endothermic or Exothermic Processes
Notice the molar enthalpy change for Sample Problem B. This enthalpy change
is positive, which means that the heating of a sample requires energy. So, the
heating of a sample is an endothermic process. In contrast, the cooling of a sam-
ple releases energy or has a negative enthalpy change and is an exothermic
process, such as the process in Sample Problem C. In fact, you can use enthalpy
Changes to determine if a process is endothermic or exothermic. Processes that
ave positive enthalpy changes are endothermic and processes that have nega-
Transcribed Image Text:To dete tive enthalpy changes are exothermic. mole. The enthalpy value is negative, which indicates a cooling process. The calculation shows the molar enthalpy change has units of joules per lpy change, use the equation AH = CAT. final value, initial valu- Calculate. than the fi AH = CAT (24.2 J/K•mol)(-15 K) = -360 J/mol Verify your results. PRACTICE The molar heat capacity of Al(s) is 24.2 J/K•mol. Calculate the molar onthalpy change when Al(s) is cooled from 128.5°C to 22.6°C. Lead has a molar heat capacity of 26.4 J/K•mol. What molar enthalpy PRO SO S change occurs when lead is cooled from 302°C to 275°C? 3 Calculate the molar enthalpy change when mercury is cooled 10 K. The molar heat capacity of mercury is 27.8 J/K•mol. Enthalpy Changes of Endothermic or Exothermic Processes Notice the molar enthalpy change for Sample Problem B. This enthalpy change is positive, which means that the heating of a sample requires energy. So, the heating of a sample is an endothermic process. In contrast, the cooling of a sam- ple releases energy or has a negative enthalpy change and is an exothermic process, such as the process in Sample Problem C. In fact, you can use enthalpy Changes to determine if a process is endothermic or exothermic. Processes that ave positive enthalpy changes are endothermic and processes that have nega-
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