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  • Given: - The heat of fusion for a substance is <img alt="\mathrm{120 \mathrm{~J} / \mathrm{g}.}" src=

Given: - The heat of fusion for a substance \mathrm{Z} is \mathrm{120 \mathrm{~J} / \mathrm{g}.}

- The heat of vaporization for substance Z is \mathrm{550 \mathrm{~J} / \mathrm{g}.}

- The molar mass of substance \mathrm{Z} is \mathrm{40 \mathrm{~g} / \mathrm{mol}.}

- Initial temperature of substance \mathrm{Z} is\mathrm{ -10^{\circ} \mathrm{C}.}

- Final temperature of the vaporized substance \mathrm{Z} is \mathrm{ 120^{\circ} \mathrm{C}.}

- The specific heat capacity of substance \mathrm{Z} (liquid) is \mathrm{ 5.0 \mathrm{~J} / \mathrm{g}^{\circ} \mathrm{C}.}

- The specific heat capacity of vaporized substance \mathrm{Z} is \mathrm{2.0 \mathrm{~J} / \mathrm{g}^{\circ} \mathrm{C}.}

Calculate the enthalpy change for the following process: Heating 25 \mathrm{~g} of substance \mathrm{Z} at \mathrm{-10^{\circ} \mathrm{C}} to vaporized substance \mathrm{Z} at \mathrm{120^{\circ} \mathrm{C}.}

Option: 1

19250kJJ


Option: 2

19250J


Option: 3

-500kJ


Option: 4

-250kJ


Answers (1)

best_answer

Step 1: Calculate the heat required to raise the temperature of substance \mathrm{Z} from\mathrm{ -10^{\circ} \mathrm{C}} to \mathrm{0^{\circ} \mathrm{C}.}

                                          \mathrm{ q_1=m \times C_{\mathrm{Z}, \text { liquid }} \times \Delta T }

Where: \mathrm{-m=25 \mathrm{~g}} (mass of substance \mathrm{\mathrm{Z}} ) \mathrm{-C_{\mathrm{Z} \text {, liquid }}=5.0 \mathrm{~J} / \mathrm{g}^{\circ} \mathrm{C} } (specific heat capacity of substance \mathrm{\mathrm{Z})-\Delta T=0-(-10)^{\circ} \mathrm{C}=10^{\circ} \mathrm{C}}

                                      \mathrm{ q_1=25 \mathrm{~g} \times 5.0 \mathrm{~J} / \mathrm{g}^{\circ} \mathrm{C} \times 10^{\circ} \mathrm{C}=1250 \mathrm{~J} }

Step 2: Calculate the heat required to melt substance \mathrm{Z} at \mathrm{0^{\circ} \mathrm{C}} to substance \mathrm{Z} at \mathrm{0^{\circ} \mathrm{C}.}

                                             \mathrm{ q_2=m \times \Delta H_{\text {fusion }} }

Where: \mathrm{-m=25 \mathrm{~g}} (mass of substance \mathrm{Z} ) \mathrm{-\Delta H_{\text {fusion }}=120 \mathrm{~J} / \mathrm{g}} (heat of fusion for substance Z)

                                          \mathrm{ q_2=25 \mathrm{~g} \times 120 \mathrm{~J} / \mathrm{g}=3000 \mathrm{~J} }

Step 3: Calculate the heat required to raise the temperature of substance \mathrm{Z} from \mathrm{0^{\circ} \mathrm{C}} to \mathrm{120^{\circ} \mathrm{C}.}

                                           \mathrm{ q_3=m \times C_{\mathrm{Z}, \text { liquid }} \times \Delta T }

Where: \mathrm{-m=25 \mathrm{~g}} (mass of substance \mathrm{\mathrm{Z}} ) \mathrm{-C_{\mathrm{Z}}, liquid =5.0 \mathrm{~J} / \mathrm{g}^{\circ} \mathrm{C}} (specific heat capacity of substance \mathrm{\mathrm{Z})-\Delta T=120^{\circ} \mathrm{C}-0^{\circ} \mathrm{C}=120^{\circ} \mathrm{C}}

                                          \mathrm{ q_3=25 \mathrm{~g} \times 5.0 \mathrm{~J} / \mathrm{g}^{\circ} \mathrm{C} \times 120^{\circ} \mathrm{C}=15000 \mathrm{~J} }

The total heat for the process is \mathrm{q_{\text {total }}=q_1+q_2+q_3=1250 \mathrm{~J}+3000 \mathrm{~J}+ 15000 \mathrm{~J}=19250 \mathrm{~J}.}

So, option B is correct

Posted by

Gaurav

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