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$$
\text { A I-kg block of iron is heated from } 25 \text { to } 75^{\circ} \mathrm{C} \text { . What is the change in the iron's total internal energy and enthalpy? }
$$

$$
A-3 b \longrightarrow c=0.45 \mathrm{kJ} / \mathrm{kg} . \mathrm{k}
$$

$$
\Delta H=\Delta U
$$$$
\longrightarrow \text { Solids }
$$

\(∴ \quad \Delta H=\Delta V=m c \Delta T \)

$$
=1 * 0.45 *(75-25)
$$

$$
=\quad 22.5 \mathrm{kJ}
$$

$$
\begin{array}{l}{\text { An ordinary egg can be approximated as a } 5.5 \text { -cm- diameter sphere. }} \\ {\text { The egg is initially at a uniform temperature of } 8^{\circ} \mathrm{C} \text { and is dropped into boiling water }} \\ {\text { at } 97^{\circ} \mathrm{C} \text { . Taking the properties of the egg to be } \mathrm{p}=1020 \mathrm{kg} / \mathrm{m} 3 \text { and } \mathrm{cp}=3.32 \mathrm{kJ} / \mathrm{kg}-\mathrm{C} \text { , }}\end{array}
$$

$$
\begin{array}{l}{\text { determine how much heat is transferred to the egg by the time }} \\ {\text { the average temperature of the egg rises to } 80^{\circ} \mathrm{C} \text { . }}\end{array}
$$

$$
E_{i n-} E_{o u t}= \Delta E_{system}
$$

$$
Q_{\text { in }}=\Delta U_{\text { egg }}=m\left(u_{2}-u\right)
$$

$$
=m\left(T_{2}-T_{1}\right)
$$

$$
Q_{i n}=m c p\left(T_{2}-T_{1}\right)
$$

$$
m=\rho v=\rho+\frac{\pi D^{3}}{6}
$$$$
=(1020) \frac{\pi(0.055)^{3}}{6}=0.0889 \mathrm{kg}
$$

$$
Q_{i n}=0.0889 * 3.32(80-8)=21.2 kJ
$$

 

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