Answer:
Endothermic
4.433kJ
15.91 kJ / mol
Explanation:
In water, ammonium chloride dissolves thus:
NH₄Cl(s) → NH₄⁺(aq) + Cl⁻(aq)
As the student observed the temperature decreased, the reaction is <em>endothermic </em>because absorbs heat from surroundigns when occurs.
It is possible to find the absorbed heat using coffee cup calorimeter equation:
Q = m×C×ΔT
<em>Where Q is heat, m is mass of solution (250g + 14.9g = 264.9g), C is specific heat of solution (It is possible to assume specific heat of pure water, 4.184J/g°C), and ΔT is change in temperature (20.0°C-16.0°C = 4.0°C)</em>
Replacing:
Q = 264.9g×4.184J/g°C×4.0°C
Q = 4433 J = <em>4.433kJ</em>
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As enthalpy is the change in heat per mole of reaction, moles of ammonium chloride that reacted were:
14.9g NH₄Cl × (1mol / 53.491g) = <em>0.2786 moles</em>
As heat produced per 0.2786moles were 4.433kJ, heat per mole of ammonium chloride is:
4.433kJ / 0.2786mol = <em>15.91 kJ / mol</em>
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