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14 November, 00:26

When 16.9 g KOH is dissolved in 90.8 g of water in a coffee-cup calorimeter, the temperature rises from 18.5 °C to 34.27 °C. What is the enthalpy change per gram (in J/g) of KOH dissolved in the water? Assume that the solution has a specific heat capacity of 4.18 J/g*K. Water has a density of 1.00 g/ml. Be sure to enter the correct sign (+/-). Enter to 1 decimal place.

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  1. 14 November, 03:04
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    -431.5 J/g

    Explanation:

    Mass of solution = Mass of solute + mass of solvent

    Solute is KOH while solvent is water.

    Mass of KOH = 16.9 g

    Mass of water = 90.8 g

    Mass of solution = 16.9 + 90.8

    = 107.7 g

    Change in temperature (Δt) = 34.27 - 18.5

    = 16.2 °C

    Heat required to raise the temperature of water is released by dissolving KOH.

    Therefore,

    Heat released by KOH = m * s * Δt

    = 107.7 * 4.18 * 16.2

    = 7293 J

    Heat released by per g KOH = 7293 J/16.9 g

    = 431.5 J/g

    As heat is released therefore, enthalpy change would be negative.

    Enthalpy change of KOH = - 431.5 J/g
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