Waec Model Questions Vol1 2021 Chemistry Question 6

Practice essay / theory question 6 from the 2021 Waec Model Questions Vol1 Chemistry examination. This question covers States of Matter, Phase changes, Enthalpy, Specific heat .

Waec Model Questions Vol1 2021 Chemistry Essay / Theory
Topics: States of Matter Phase changes Enthalpy Specific heat
Question 6 WAEC_MODEL_QUESTIONS_VOL1 • 2021 • CHEMISTRY • essay

Water undergoes several phase changes under standard atmospheric pressure (1 atm). The following data are given: • Specific heat capacity of ice, c₁ = 2.09 J g⁻¹ K⁻¹ (for –10 °C to 0 °C) • Specific heat capacity of liquid water, c₂ = 4.18 J g⁻¹ K⁻¹ (for 0 °C to 100 °C) • Specific heat capacity of steam, c₃ = 2.01 J g⁻¹ K⁻¹ (for 100 °C to 120 °C) • Enthalpy of fusion of water, ΔH_fus = 334 J g⁻¹ • Enthalpy of vaporisation of water, ΔH_vap = 2260 J g⁻¹ A sample of 150.0 g of ice at –10 °C is heated until it becomes steam at 120 °C. Answer the following questions:

Question Parts

( a )
Calculate the total amount of heat energy (in kJ) required to convert the 150.0 g of ice at –10 °C to steam at 120 °C. Show all steps.
( b )
If the pressure were increased to 2 atm, explain qualitatively how the boiling point of water would change and why this would affect the total heat calculated in part (a).
( c )
A student mistakenly uses the specific heat capacity of liquid water (c₂) for the entire temperature range (–10 °C to 120 °C) and ignores the latent heats. Estimate the percentage error in the total heat calculated compared with the correct value from part (a).

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About This Question

This is Waec Model Questions Vol1 2021 Chemistry Question 6. It is one of the essay questions from the 2021 Waec Model Questions Vol1 Chemistry examination.

The question covers States of Matter, Phase changes, Enthalpy, Specific heat .

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