Question

10) Which of the following statements are correct?

A) Turning up the flame under a pan of boiling water increases the water temperature so that it boils faster.

B) Sweating is an important bodily function in which heat is extracted to regulate the body temperature.

C) On a cold day, a piece of metal feels much colder than a piece of wood due the differences in their specific heats.

D) In a fixed container holding oxygen (32u) and helium (4u) gases at the same temperature the molecules have the same average speed.

E) The heat required to condense a gaseuos substance into its liquid state is called latent heat of vaporization

F) The measure of the average kinetic energy of individual molecules is referred to as temperature.

Answer 1

(a):

correct:

reason:

greater the flame more the heat will be transferred hence temp of water increases faster and hence it boils faster

(B):

correct.

Reason: the external temp. envolves the external heat in evopration of the sweat due to this the external heat doesn't reach the human body hence this process regulates the body temprature.

(C):

correct

Reason: When you put your finger on an object that is colder than the surface of your finger, heat energy will be transferred from the surface of your finger into the surface of the object, until the temperatures are equalized, by the process of conduction. At the same time, heat energy will be transferred from the interior of your finger to the cooling surface of your finger, and heat energy will be transferred from the warming surface of the object into the interior of the object. The rate of energy transfer will depend on the difference in temperature - large temperature differences will accelerate the energy transfer, but as the temperatures become closer, the rate will slow down.

The amount of energy you need to put into a fixed mass of a material to warm it up by a certain temperature increment is known as the material's specific heat capacity. Let's look at two common metals. Aluminum has a specific heat capacity of 0.90 J/(g?K) - that is, you need to put 0.90 J into 1 g of aluminum to raise its temperature by 1 K (remember that an increment of 1 Kelvin is the same as an increment of 1 degree Celsius). Steel has a specific heat capacity of 0.49 J/(g?K). Wood, on the other hand, has a specific heat capacity of about 1.7 J/(g?K) (with a range of between 1.2 and 2.3 J/(g?K), depending on the species of wood and how dry it is).

Let's assume for a moment that your finger is entirely at one temperature, and the object is entirely at a lower temperature - and as the temperatures of your finger and the object equilibrate, the temperature in each remains uniform. So, assuming you have equal masses of wood and metal, you need to put more energy into the wood to raise its temperature - maybe 2 to 4 times as much energy. That means the temperature of the wood will raise more slowly, so the equilibrium temperature of your finger and the wood will be lower.

But your finger and the object do not have uniform temperatures. The thermal energy transferred from the surface of your finger to the surface of the object will be conducted through the object, at a rate determined by the conductivity of the object. The thermal conductivity of aluminum is about 225 W/(m?K) - remember that a watt (unit of power) is equal to a Joule (unit of energy) per second, so we're saying that if you have a bar of aluminum 1 meter long, with one end at a temperature 1 Kelvin higher than the other end, the rate of energy transfer from one end of the bar to the other will be 225 Joules per second. Steel has a thermal conductivity of about 45 W/(m?K). The thermal conductivity of wood is about 0.2 W/(m?K). So, thermal energy moves much more slowly in wood than it does in metal - about 200 times more slowly than steel, and 1000 times more slowly than aluminum!

What that means is, when you put your finger on wood, you're going to warm up a very small mass of wood near the contact area, and the thermal energy won't move away from that spot very quickly. So, that small mass of wood will come nearly into thermal equilibrium with your finger very rapidly, at a temperature near the temperature your finger started at. If you wait a very long time, the thermal energy will move out into the rest of the wood, slowing bringing down the equilibrium temperature, but your body is generating heat energy to warm your finger back up to it's normal point that whole time.

But when you put your finger on metal, because the thermal energy is being conducted through the metal quickly, you're warming up a much larger mass of metal. Even though metal has a lower specific heat, when you multiply that by a much larger mass, you require more energy! So the temperature of the metal rises more slowly, and the equilibrium temperature of your finger and the metal will be closer to the original temperature of the metal.

(d):

wrong

Reason:

v(avg) directly praportional to sqrt( (3*R*T) / M )

since mass of O2 and H2 are different therefore

v(avg) would be different.

(e):

wrong

latent eat of vapourisation = heat require to change liq into gas

though numerically they are equal but still in one case heat is absorbed and in other heat is evolved.

(f):

right

Reason

for ideal gas

KE avg = (3/2)*k*T

so one can say that if we know temp we know the avg. KE.