"During a change in state the heat energy is used to change the bonding between the molecules. In the case of melting, added energy is used to break the bonds between the molecules. In the case of freezing, energy is subtracted as the molecules bond to one another. These energy exchanges are not changes in kinetic energy. They are changes in bonding energy between the molecules.
"If heat is coming into a substance during a phase change, then this energy is used to break the bonds between the molecules of the substance. The example we will use here is ice melting into water. Immediately after the molecular bonds in the ice are broken the molecules are moving (vibrating) at the same average speed as before, so their average kinetic energy remains the same, and, thus, their Kelvin temperature remains the same."
Changing state A substance must absorb heat energy so that it can melt or boil. The temperature of the substance does not change during melting, boiling or freezing, even though energy is still being transferred. A heating curve is a graph showing the temperature of a substance plotted against the amount of energy it has absorbed. You may also see a cooling curve, which is obtained when a substance cools down and changes state. A heating curve for ice Notice that the temperature stays the same during a change of state, melting or boiling, even though heat energy is still being absorbed. The temperature also stays the same while a liquid freezes, even though heat energy is still being released to the surroundings. Specific latent heat The specific latent heat of a substance is a measure of how much heat energy is needed to melt or boil it. It is the energy needed to melt or boil 1 kg of the substance. Different substances have different specific latent heats. The specific latent heat of a given substance is different for boiling than it is for melting. |
The temperature of a substance does not change as the substance boils. Write two or three...
1. When a heated substance melts or boils, its temperature does not increase until all of the substance has melted or boiled. Why? 2. Why does placing a magnet next to an object made of iron for a long period of time make the iron piece magnetic?
How does the molar entropy of a substance change with increasing temperature? A) The molar entropy of a substance increases with increasing temperatures. B) The molar entropy of a substance decreases with increasing temperatures.
what happens to the conductivity of a substance if you increase the temperature of the solution. Explain what happens on a molecular level during this temperature increase.
Compare and contrast the three phases of matter and give an example of a substance in each phase. Based on kinetic molecular theory, what happens to the kinetic energy of the molecules of a substance as it goes from solid to liquid to gas?From a molecular point of view, explain why evaporation is a cooling process. What cools? Give an example.From a molecular point of view, explain why condensation is a warming process. What warms? Give an example.Why is a...
Room-temperature water boils spontaneously in a vacuum- on the Moon, for example. Could you cook an egg in this boiling water? Explain Find what heat in calories (cal) is required to increase the temperature of 60 g water from 0°C to 55°C. The specific heat capacity of water is 1 cal/ g•°C. Express your answer to two significant figures and include the appropriate units.
Which substance in the table below undergoes the greatest temperature change when the same mass of each substance absorbs the same amount of heat? substance specific / heat (J/(g⋅0C) N2 (g) / 1.04 C2H5OH (l) / 2.42 H2O (l) / 4.18 CH4 (g) / 2.20
Consider these two substances: Substance J is at temperature T = 880 K, and substance K is at T = 990 K. They are in thermal contact. Substance J actually heats up Substance K. True False
Consider these two substances: Substance J is at temperature T = 880 K, and substance K is at T = 990 K. They are in thermal contact. Substance J actually heats up Substance K. True False
"igure 1.2 Comparison of the Three Common Temperature Scales 373K 100°C 212F - Water Boils 100 degrees — 100 degrees 180 degrees 98.6°F Normal Body Temperature - Water Freezes 273K 0°C 327 Kelvin Celsius Fahrenheit Graphical Question 1.2 The following Celsius vs. Fahrenheit data is obtained. 0.0 10.0 25.0 100.0 32.0 50.0 77.0 212.0 Using excel plot the data and determine the equation that relates Fahrenheit to Celsius.
Consider a sample of carbon dioxide solid at room temperature and pressure. This substance will change from solid to a gas under these conditions. Which of the following is correct about this change of state? A) melting, exothermic B) melting, endothermic C) sublimation, exothermic D) sublimation, endothermic