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    The standard enthalpy change for the reaction of calcium hydroxide withhydrochloric acid was found by reacting 0.0100 mol of solid calcium hydroxidewith 50.0 cm3 of a 1.00 mol dm–3 solution of hydrochloric acid (an excess), in apolystyrene cup. The temperature rose from 21.2 °C to 26.7 °C.
    • Q) The experiment was repeated again using 25 cm3 of 2.00 mol dm3 hydrochloric
      acid. Predict the temperature change in this experiment.
    • I wrote that the temperature change would not be different, because the volume is 2x less but the concentration is 2x greater, -- this was wrong, the temperture change doubles
    • can someone explain why
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    (Original post by qatarownz)
    The standard enthalpy change for the reaction of calcium hydroxide withhydrochloric acid was found by reacting 0.0100 mol of solid calcium hydroxidewith 50.0 cm3 of a 1.00 mol dm–3 solution of hydrochloric acid (an excess), in apolystyrene cup. The temperature rose from 21.2 °C to 26.7 °C.
    • Q) The experiment was repeated again using 25 cm3 of 2.00 mol dm3 hydrochloric
      acid. Predict the temperature change in this experiment.
    • I wrote that the temperature change would not be different, because the volume is 2x less but the concentration is 2x greater, -- this was wrong, the temperture change doubles
    • can someone explain why
    The energy change would be the same, but you are heating up a smaller mass of liquid.

    ΔE = mcΔT

    If ΔE, and c are constant

    Then ΔT is inversely proportional to m

    i.e. if the mass halves, the temperature doubles
 
 
 
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