Unit 3 Thermal Physics

Energy is transferred to water in a flask at a rate P. The water reaches boiling point and then P is increased. What are the changes to the temperature of the water and to the rate of vaporization of the water after the change?

• A

• B

• C

• D

Boiling water is heated in a 2 kW electric kettle. The initial mass of water is 0.4 kg. Assume the specific latent heat of vaporization of water is 2 MJ kg^–1.

What is the time taken for all the water to vaporize?

• 250 s

• 400 s

• 2500 s

• 4000 s

Tags

NGSS.HS-PS3-1

NGSS.HS-PS3-4

A gas storage tank of fixed volume V contains N molecules of an ideal gas at temperature T. The pressure at kelvin temperature T is 20 MPa. 
 $\frac{N}{4}$   molecules are removed and the temperature changed to 2T. What is the new pressure of the gas?

• 10 MPa

• 15 MPa

• 30 MPa

• 40 MPa

A substance changes from the solid phase to the gas phase without becoming a liquid and without a change in temperature.

What is true about the internal energy of the substance and the total intermolecular potential energy of the substance when this phase change occurs?

• A

• B

• C

• D

The temperature of a fixed mass of an ideal gas changes from 200 °C to 400 °C.What is 
 $\frac{mean\ kinetic\ energy\ of\ gas\ at\ 200\degree C}{mean\ kinetic\ energy\ of\ gas\ at\ 400\degree C}$  

• 0.50

• 0.70

• 1.4

• 2.0

A liquid of mass m and specific heat capacity c cools. The rate of change of the temperature of the liquid is k. What is the rate at which thermal energy is transferred from the liquid?

• $\frac{mc}{k}$

• $\frac{k}{mc}$

• $\frac{1}{kmc}$

• $kmc$

A 700 W electric heater is used to heat 1 kg of water without energy losses. The specific heat capacity of water is 4.2 kJ kg^–1 K^–1. What is the time taken to heat the water from 25 °C to 95 °C?

• 7 s

• 30 s

• 7 minutes

• 420 minutes

Tags

NGSS.HS-PS3-1

NGSS.HS-PS3-4

A container is filled with a mixture of helium and oxygen at the same temperature. The molar mass of helium is 4 g mol–1 and that of oxygen is 32 g mol–1.What is the ratio  $\frac{average\ speed\ of\ helium\ molecules}{average\ speed\ of\ oxygen\ molecules}$  

•  $\frac{1}{8}$  

•  $\frac{1}{\sqrt{8}}$  

•  $\sqrt{8}$  

•  $8$  

Container X contains 1.0 mol of an ideal gas. Container Y contains 2.0 mol of the ideal gas. Y has four times the volume of X. The pressure in X is twice that in Y.
What is
 $\frac{temperature\ of\ gas\ inX}{temperature\ ofgas\ inY}$  ?

•  $\frac{1}{4}$  

•  $\frac{1}{2}$  

• 1

• 2

A solid substance has just reached its melting point. Thermal energy is supplied to the substance at a constant rate. Which graph shows the variation of the temperature T of the substance with energy E supplied?

• A

• B

• C

• D