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tatuchka [14]
2 years ago
5

A scientist measures the standard enthalpy change for the following reaction to be -17.2 kJ : Ca(OH)2(aq) 2 HCl(aq)CaCl2(s)

Chemistry
1 answer:
elixir [45]2 years ago
8 0

Answer: \Delta H^{0}=-173.72 kJ/mol

Explanation: <u>Enthalpy</u> <u>Change</u> is the amount of energy in a reaction - absorption or release - at a constant pressure. So, <u>Standard</u> <u>Enthalpy</u> <u>of</u> <u>Formation</u> is how much energy is necessary to form a substance.

The standard enthalpy of formation of HCl is calculated as:

\Delta ^{0}=\Sigma H_{products}-\Sigma H_{reactants}

Ca(OH)_{2}_{(aq)}+2HCl_{(aq)} → CaCl_{2}_{(s)}+2H_{2}O_{(l)}

Standard Enthalpy of formation for the other compounds are:

Calcium Hydroxide: \Delta H^{0}= -1002.82 kJ/mol

Calcium chloride: \Delta H^{0}= -795.8 kJ/mol

Water: \Delta H^{0}= -285.83 kJ/mol

Enthalpy is given per mol, which means we have to multiply by the mols in the balanced equation.

Calculating:

-17.2=[-795.8+2(285.85)]-[-1002.82+2\Delta H]

-17.2=-1367.46+1002.82-2\Delta H

2\Delta H=17.2-364.64

\Delta H=-173.72

So, the standard enthalpy of formation of HCl is -173.72 kJ/mol

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Hydrogen Chloride Gas is heavier than air and sinks to the ground after being released. Firefighters closer to the ground will be subjected to significantly greater concentrations of hydrogen chloride gas than the firefighters walking on top of railcars.

Explanation:

The molar mass of air is 28.97 g/mol. Air is approximately 78% N2, which has a molar mass of 28.014 g/mol and 21% oxygen, which has a molar mass of 32 g/mol; the remaining constituents of air include CO2 and other trace amounts of gases.

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The height of railway cars is reported to vary between 13.5 ft to 15.5 ft. So firefighters on tank cars are generally above the HCl gas (although localized atmospheric conditions could cause the HCl to move higher up in the air column).

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