Chemistry, 26.07.2019 13:00 jacamron

Assume your calorimeter is not perfect. burning 0.51 g of ethanol resulted in a 10 degree c rise in the temperature of the 200 ml of water in your calorimeter. how much energy was released by burning 0.51 g of ethanol? select one: a. 1386.1 kj b. 0.15 kj c. 29.4 kj d. 15.2 kj

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Answer from: oglilbrandon

The energy released by burning 0.15 g of ethanol is $\boxed{{\text{d}}{\text{. 15}}{\text{.2 kJ}}}$ .

Further explanation:

Enthalpy is defined as a state function and therefore its value depends upon the initial and final state of the system but not upon the path. This is the reason that the overall reaction can be simply obtained by adding or subtracting the enthalpy change of the individual steps utilized to get the final reaction. Enthalpy change is the amount of energy released or absorbed during a chemical reaction. It is denoted by $\Delta{\text{H}}$ .

Combustion reactions are those reactions in which a compound is burned in presence of air to form water and carbon dioxide.

Example of combustion reactions are as follows:

(a) ${\text{C}}{{\text{H}}_4}+{{\text{O}}_2}\to{\text{C}}{{\text{O}}_2} + {{\text{H}}_2}{\text{O}}$

(b) ${{\text{C}}_{10}}{{\text{H}}_{14}}+12{{\text{O}}_2}\to10{\text{C}}{{\text{O}}_2}+4{{\text{H}}_2}{\text{O}}$

Enthalpy change of combustion reaction is the amount of energy released when 1 mole of compound is burned in excess of oxygen at standard temperature and pressure to form carbon dioxide and water.

The balanced chemical reaction is written as follows:

${{\text{C}}_2}{{\text{H}}_5}{\text{OH}}+{\text{3}}{{\text{O}}_2}\to{\text{2C}}{{\text{O}}_2}+3{{\text{H}}_2}{\text{O}}$

According to the stoichiometric of reaction, 1 mole of ethanol reacts with 3 moles of oxygen molecule to form 2 moles of carbon dioxide and 3 moles of water.

The expression to calculate the number of moles is as follows:

${\text{number of moles}}=\frac{{{\text{mass of }}{{\text{C}}_2}{{\text{H}}_5}{\text{OH}}}}{{{\text{molar mass of }}{{\text{C}}_2}{{\text{H}}_5}{\text{OH}}}}$ …… (1)

Given mass of ${{\text{C}}_2}{{\text{H}}_5}{\text{OH}}$ is 0.15 g.

Molar mass of ${{\text{C}}_2}{{\text{H}}_5}{\text{OH}}$ is 46.07 g.

Substitute these value in the equation (1).

$\begin{aligned}{\text{number of moles}}&=\frac{{0.51{\text{ g}}}}{{46.07{\text{ g/mol}}}}\\&=0.011{\text{ mol}}\\\end{aligned}$

The enthalpy of combustion of ethanol at ${\mathbf{25}}\;{\mathbf{^\circ C}}$ is ${\mathbf{1386 kJ/mol}}$ .

The formula to calculate amount of energy released is as follows:

${\text{Amount of energy}}={\text{number of moles}}\times{\text{enthalpy }}$ …… (2)

Substitute 0.011 mol for number of moles and ${\text{1386 kJ/mol}}$ for enthalpy change in equation (2)

$\begin{aligned}{\text{Amount of energy}}&=0.011{\text{ mol}}\times{\text{1386 kJ/mol}}\\&=15.246{\text{ kJ}}\\&\approx15.2{\text{ kJ}}\\\end{aligned}$

Therefore, the amount of energy released is ${\mathbf{15}}{\mathbf{.2 kJ}}$ .

Learn more:

1. Determine coefficients needed to balance the equation for the complete combustion of methane?link

2. How much energy required to break the hydrogen bond?link

Answer details:

Grade: Senior school

Subject: Chemistry

Chapter: Thermodynamics

Keywords: Energy, number of moles, enthalpy, enthalpy change, combustion reaction, released, absorbed, standard, temperature, pressure, chemical reaction, 15.2 kj, 0.011 mol and 1386 kj.