Question

a simple constant - pressure calorimeter can be made from a foam coffee cup and a thermometer. energy changes in a reaction are observed via a temperature change of the solution in the cup. bomb calorimeters are used to measure combustion and other gas - producing reactions, where the reaction is observed in a strong, sealed vessel. the idea behind calorimeters is that if they are sufficiently insulated from the outside environment, any energy gained or lost in the chemical reaction will be directly observable as a temperature and/or pressure change in the calorimeter.

part a
a total of 2.00 mmol of a compound is allowed to react with water in a foam coffee cup and the reaction produces 117 g of solution. the reaction caused the temperature of the solution to rise from 21.00 to 24.70 °c. what is the enthalpy of this reaction? assume that no heat is lost to the surroundings or to the coffee cup itself and that the specific heat of the solution is the same as that of pure water.
enter your answer in kilojoules per mole of compound to three significant figures.
view available hints?
δh = kj/mol

Explanation:

Step1: Calculate heat absorbed by solution

Use the formula $q = mc\Delta T$. The mass of solution $m = 117\ g$, specific - heat capacity of water $c= 4.184\ J/(g\cdot^{\circ}C)$, and $\Delta T=T_2 - T_1=24.70^{\circ}C - 21.00^{\circ}C = 3.70^{\circ}C$. So $q=(117\ g)\times(4.184\ J/(g\cdot^{\circ}C))\times(3.70^{\circ}C)$
$q = 117\times4.184\times3.70\ J=117\times15.4808\ J = 1811.2536\ J$.

Step2: Convert heat to kJ

$q = 1811.2536\ J\times\frac{1\ kJ}{1000\ J}=1.8112536\ kJ$.

Step3: Calculate enthalpy change per mole

The number of moles of the compound $n = 2.00\ mmol=2.00\times10^{- 3}\ mol$. The enthalpy change $\Delta H=\frac{q}{n}$. So $\Delta H=\frac{1.8112536\ kJ}{2.00\times10^{-3}\ mol}=905.6268\ kJ/mol$.
Rounding to three significant figures, $\Delta H = 906\ kJ/mol$.

Answer:

$906\ kJ/mol$