Chemistry, 29.10.2019 04:31 tjmoney7709

The sun delivers roughly 1kwm2 of power to the earth’s surface. a parabolic mirror with a 1.5 m radius is used to focus this energy onto a beaker containing 2 l of water. estimate the time taken by the mirror to rise the temperature of water by 60°c, assuming cp, m= 75291 j k mol and ignoring energy losses to the surroundings.

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Answer from: beverlyamya

Explanation:

The amount of heat required by water to increase its temperature by $60^{o}C$ ,

q = $m \times c dT$ .............. (1)

where, q = heat gained

m= mass in kg,

c = specific heat (in terms of $kJ/ kg^{o}C$ )

dT = increase in temperature

Now, putting the given values into equation ( 1) as follows.

q = $m \times c dT$

= $1 kg \times (75.291 kJ/ kg^{o}C) \times 60^{o}C$

= 4517.46 kJ

Now, surface area of the mirror, A = $\pi \times r^{2}$

where, r = radius of the mirror

= 1.5 m

Therefore, area = $\pi \times r^{2}$

= $3.14 \times (1.5 m)^{2}$

= 7.065 $m^{2}$

As, 1 $Kw m^{2}$ means = 1 kJ per second per square meter surface area. (as 1 W = 1 J/s)

Hence, amount of energy focused by mirror = incidence rate of solar energy x surface area of mirror

= $1 kJ/s m^{2} \times 3.14 m^{2}$

= 3.14 kJ s-1

Therefore, the mirror focuses 3.14 kJ energy per second

Time required by the mirror to focus 4517.46 kJ energy = $\frac{4517.46 kJ
}{3.14 kJ/s}$

= 1438.68 seconds

or, = $\frac{1438.68 sec}{60 sec/min}$

= 23.97 min

Thus, we can conclude that the time taken by the mirror to rise the temperature of water is 23.97 min.

Answer from: Quest

Answer : option c) heat is released during the process.explanation :

the enthalpy of formation of water is given as -285.8kj/mol, which states that the enthalpy of formation is negative.

negative enthalpy of formation indicates that the heat is released during the reaction process. the heat is released from reaction to the surroundings the enthalpy is expressed with a negative sign with the energy given out in the reaction process.

the formation of water takes place by giving out heat which is -285.8 kj/mol.

Answer from: Quest

You would be correct, boiling water does disinfect contamination. the property of disinfecting means to kill germs, bacteria and other pathogens or contamination that might cause an infection or cause a person to become sickly. a couple methods of disinfecting are using soap, other cleaning supplies or by simply "boiling" the contaminate. the reason why boiling water disinfects certain attributes is because some cells cannot survive the heat and pressure.

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The sun delivers roughly 1kwm2 of power to the earth’s surface. a parabolic mirror with a 1.5 m radi...