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# Chemistry question Edexcel

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1. 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
2. (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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