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Experimental Enthalpy Changes

Experimental Enthalpy Changes. q = mc Δ t. Copper Sulphate + Zinc. 25cm 3 of 0.5 mol dm -3 CuSO 4 1g zinc (excess) Temp rise 20 o C. Temp. Time (min). Calculate heat energy. q = m c Δ t. q = heat energy change (J) m = 25g (assuming density = 1g/cm 3 ) c = 4.18Jg -1 K -1 Δ t = 20.

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Experimental Enthalpy Changes

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  1. Experimental Enthalpy Changes q = mcΔt

  2. Copper Sulphate + Zinc • 25cm3 of 0.5 mol dm-3 CuSO4 • 1g zinc (excess) • Temp rise 20oC Temp Time (min)

  3. Calculate heat energy q = m c Δt q = heat energy change (J) m = 25g (assuming density = 1g/cm3) c = 4.18Jg-1K-1 Δt = 20 q = 25 x 4.18 x 20 q = 2090 J = 2.09 kJ

  4. Calculate no moles used n = c x v n = no moles v = volume used (dm-3) c = concentration (0.5 moldm-3) n = 0.5 x 25/1000 n = 0.0125

  5. Calculate ΔH in kJmol-1 ΔH = q / n n = no moles q = energy change (kJ) ΔH = 2.09 / 0.0125 ΔH = - 167.2 kJmol-1 exothermic

  6. Citric Acid & Sodium hydrogen Carbonate • 25cm3 of 0.4 mol dm-3 citric acid • 3g NaHCO3 (excess) • Temp drop 9oC

  7. Calculate heat energy q = m c Δt q = heat energy change (J) m = 25g (assuming density = 1g/cm3) c = 4.18Jg-1K-1 Δt = 9 q = 25 x 4.18 x 9 q = 940.5 J = 0.9405 kJ

  8. Calculate no moles used n = c x v n = no moles v = volume used (dm-3) c = concentration (0.5 moldm-3) n = 0.4 x 25/1000 n = 0.01

  9. Calculate ΔH in kJmol-1 ΔH = q / n n = no moles q = energy change (kJ) ΔH = 0.9405 / 0.01 ΔH = + 94 kJmol-1 endothermic

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