A Substance Has a Melting Point of 20°C and a Heat

question 75

Multiple Choice

A substance has a melting point of 20°C and a heat of fusion of $3.6 \times 10^4 \mathrm {~J} / \mathrm { kg }$ The boiling point is $150 ^ { \circ } \mathrm { C }$ and the heat of vaporization is $7.2 \times 10^4 \mathrm {~J} / \mathrm { kg }$ at a pressure of one atmosphere.The specific heats for the solid,liquid,and gaseous phases are 600 J/kg ∙ K (solid) ,1000 J/kg ∙ K (liquid) ,and 400 J/kg ∙ K (gaseous) .How much thermal energy is emitted by $2.80 \mathrm {~kg}$ of this substance when it is cooled from 170°C to 86°C at a pressure of one atmosphere?

• A)400 kJ
• B)200 kJ
• C)300 kJ
• D)440 kJ
• E)640 kJ

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