Thermochemistry Examples

A concrete block has mass $5000\,\text{kg}$. For this exercise, use the stated specific heat $c=0.880\,\text{J}/(\text{g}\cdot^\circ\text{C})$. Calculate the sensible heat change when it cools from $40.0^\circ\text{C}$ to $20.0^\circ\text{C}$.

For the reaction

use the stated exercise inputs $\Delta H_f^\circ[CO_2(g)]=-393.5\,\text{kJ/mol}$, $\Delta H_f^\circ[H_2O(l)]=-285.8\,\text{kJ/mol}$, $\Delta H_f^\circ[CH_4(g)]=-74.8\,\text{kJ/mol}$, and $\Delta H_f^\circ[O_2(g)]=0$. Find $\Delta H_{\text{rxn}}^\circ$ for the reaction as written.

How much heat is absorbed by $500.0\,\text{g}$ of water heated from $20.0^\circ\text{C}$ to $60.0^\circ\text{C}$? Use the stated exercise value $c=4.184\,\text{J}/(\text{g}\cdot^\circ\text{C})$.

A reaction occurs in $100.0\,\text{g}$ of solution. Assume the solution has $c=4.184\,\text{J}/(\text{g}\cdot^\circ\text{C})$, the calorimeter hardware is negligible, and the temperature rises by $5.00^\circ\text{C}$. Find the reaction heat for the trial.

Repeat the previous $100.0\,\text{g}$ solution experiment with $\Delta T=5.00^\circ\text{C}$, but now include a calorimeter heat capacity $C_{\text{cal}}=40.0\,\text{J/K}$. Use $c_{\text{solution}}=4.184\,\text{J}/(\text{g}\cdot^\circ\text{C})$.

A target reaction can be obtained by adding two stated steps with $\Delta H_1=-50.0\,\text{kJ}$ and $\Delta H_2=+15.0\,\text{kJ}$. The intermediate species cancel when the equations are added. Find the target $\Delta H$.

A stated reaction has $\Delta H=-120\,\text{kJ}$ as written. What is $\Delta H$ when the reaction is reversed and then every coefficient is multiplied by $2$?

For

use the stated exercise inputs $\Delta H_f^\circ[CaCO_3(s)]=-1206.9\,\text{kJ/mol}$, $\Delta H_f^\circ[CaO(s)]=-635.1\,\text{kJ/mol}$, and $\Delta H_f^\circ[CO_2(g)]=-393.5\,\text{kJ/mol}$. Find the standard reaction enthalpy.