প্রশ্ন ৬৪·সময় ৩ ঘণ্টা

1. 2 litre water in a $1.5 \mathrm{~kW}$ electric kettle starts boiling after $6 \mathrm{~min} 20 \mathrm{sec}$. What was the initial temperature of water in the kettle? How many units of electricity were consumed to boil the water in the kettle? (Neglect heat losses).

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2. The elements of the third period in the Pcriodic Table are: $\mathrm{Na}, \mathrm{Mg}, \mathrm{Al}, \mathrm{Si}, \mathrm{P}, \mathrm{S}, \mathrm{Cl}, \mathrm{Ar}$. Answer the following using this information.

(a) List the elements that form nitrates.

(b) Which two of these elements form the most commonly found ionic compounds?

(c) Which element normally exists as molecules?

(d) Which element has both metallic and non-metallic properties?

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3. Given that $\mathrm{C}_{\mathrm{P}}\left(\mathrm{H}_{2}\right)=6.90 \mathrm{Cal} \mathrm{mole}^{-1} \mathrm{deg}^{-1}, \mathrm{C}_{\mathrm{P}}\left(\mathrm{O}_{2}\right)=7.05 \mathrm{Cal} \mathrm{mole}^{-1} \mathrm{deg}^{-1}$ and $\mathrm{C}_{\mathrm{p}}\left(\mathrm{H}_{2} \mathrm{O}\right)=$ $18.0 \mathrm{Cal} \mathrm{mole}{ }^{-1} \mathrm{deg}^{-1}$, Calculate the heat of formation of $\mathrm{H}_{2} \mathrm{O}$ (l) at $60^{\circ} \mathrm{C}$, if the heat of formation $2:$ $25^{\circ} \mathrm{C}$ is $-68370 \mathrm{Cal}$.

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4. A solid ball of radius $0.005 \mathrm{~m}$ and density $2.5 \times 10^{3} \mathrm{~kg} / \mathrm{m}^{3}$ is dropped into a lake water to measure its depth. The ball reached the bottom of the lake in $10 \mathrm{sec}$. If the ball attained terminal velocity in $9 \mathrm{sec}$, determine the depth of the lake. [Coefficient of viscosity water, $\eta=1.6 \times 10^{-3} \mathrm{Nsm}^{-2}$. Density of water is $1000 \mathrm{kgm}^{-3}$ ]

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5. Ammonia reacts with oxygen in accordance with the following equation:

$4 \mathrm{NH}_{3}(\mathrm{~g})+5 \mathrm{O}_{2}(\mathrm{~g})=4 \mathrm{NO}(\mathrm{g})+6 \mathrm{H}_{2} \mathrm{O}(\mathrm{g})$

At a particular moment the ammonia reacts at the rate of $0.24 \mathrm{molL}^{-1} \mathrm{~s}^{-1}$. Write the rate equation for the reaction and find the rate at which $\mathrm{H}_{2} \mathrm{O}(\mathrm{g})$ is formed.

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