First Law of Thermodynamics How is the CO 2 concentration in the atmosphere related to the melting of glaciers? How does sweating protect our bodies from overheating? Why does the thermal energy of a spoon increase when you place it in a cup of hot tea, even though no external objects do work on it? © 2014 Pearson Education, Inc.

Be sure you know how to: Identify a system and decide on the initial and final states of a process (Section 2.1). Draw an energy bar chart and use it to help apply the work-energy equation (Section 6.2). Apply your understanding of molecular motion to explain gas processes (Section 9.6). © 2014 Pearson Education, Inc.

Thermal energy of ideal gas We assumed that ideal gas particles do not interact at a distance; thus the system has no potential energy due to particle interactions. –In an ideal gas, the total internal energy of the gas particles equals its thermal energy. –The thermal energy depends only on its absolute temperature and on the number of moles of gas. © 2014 Pearson Education, Inc.

Tip © 2014 Pearson Education, Inc.

Work done on a gas Gas at high pressure pushes a piston outward, doing work. –To determine the work done by the piston on the gas, we could use calculus. –We can also identify an expression for the work done on the changing volume of gas by breaking the big volume change into many small increments and adding the work done during each small change. © 2014 Pearson Education, Inc.

Work depends on the process between the initial and final states In Figure 12.4a, to go from the initial state to the final state, the gas first has a constant volume and increasing pressure, and then has a constant pressure and decreasing volume. In Figure 12.4b, the gas first has a constant pressure/volume decrease, and then has a constant volume/pressure increase to reach the same final state. The work done for each process is different. © 2014 Pearson Education, Inc.

Tip © 2014 Pearson Education, Inc.

Work done by a gas on its environment © 2014 Pearson Education, Inc.

Prior understanding of how to change the energy of a system The total initial energy of the system plus the work done on the system by the environment equals the total final energy of the system. –The energy of the system can take many different forms. –The total energy of the system can change only if the environment does work on the system. © 2014 Pearson Education, Inc.

Observational experiments © 2014 Pearson Education, Inc. Qualitatively and Quantify Experiment

Observational experiments © 2014 Pearson Education, Inc.

Particle motion explains the change in thermal energy of the gas We need a new way to explain the change in energy of a system: –The energy of a hot flame is transferred to a gas inside a cooler cylinder without any work being done. This transfer of energy from an object at one temperature (the hot flame) to an object at a different temperature (the cool gas) is called heating. © 2014 Pearson Education, Inc.

Heating The SI unit of heating is the calorie. One calorie is the amount of energy that must be transferred to 1 g of water to increase its temperature by 1 °C. © 2014 Pearson Education, Inc.

Tip © 2014 Pearson Education, Inc.

James Joule's testing experiment © 2014 Pearson Education, Inc. Quantify and Qualitatively Describe the Experiment

James Joule's testing experiment © 2014 Pearson Education, Inc.

First law of thermodynamics The work-heating-energy equation explains many phenomena that the work-energy principle could not: –The change in the temperature of water placed on a hot electric stove –The change in the temperature of a hot hard- boiled egg placed in a bowl of cold water In all cases, the system contacts a part of the environment that is at a different temperature than the system. © 2014 Pearson Education, Inc.

A note about temperature, thermal energy, and heating Temperature is the physical quantity that measures the average random kinetic energy of the individual particles that make up the object. Thermal energy is the physical quantity that measures the total random kinetic energy of all the particles. Heating is the physical quantity that measures the process through which some amount of thermal energy is transferred. © 2014 Pearson Education, Inc.

Tip © 2014 Pearson Education, Inc.

Two important points about the quantitative analysis of heating Providing the same amount of energy to two equal amounts of a gas through heating might not lead to the same rise in the gases' temperatures if work was done on one gas but not the other. The energy that needs to be transferred through heating to change the temperature of 1 kg of air by 1 °C is different when the volume of the gas is constant versus when the pressure is constant. © 2014 Pearson Education, Inc.

The first law of thermodynamics © 2014 Pearson Education, Inc.

Tip We can rewrite the first law by including all types of energy in a system: © 2014 Pearson Education, Inc.

Observational experiments © 2014 Pearson Education, Inc. Quantify and Qualitatively Describe the Experiment

Observational experiments © 2014 Pearson Education, Inc.

Specific heat © 2014 Pearson Education, Inc.

Specific heats of various solids and liquids © 2014 Pearson Education, Inc.

Specific heat The specific heats of sand, bricks, and concrete are about one-fifth that of water. –These materials exhibit much greater temperature changes than water when equal masses of these materials absorb the same amount of energy. –This is one reason why the sand on a beach or the concrete beside a swimming pool feels so much hotter than the adjacent water on a sunny day. © 2014 Pearson Education, Inc.

Tip © 2014 Pearson Education, Inc.

Specific heat The energy ΔU must be added to a substance of mass m and specific heat c to cause its temperature to change by ΔT : © 2014 Pearson Education, Inc.

Sharing energy through the process of heating when objects are in contact A hot object loses thermal energy to a cold object through the process of heating, and a cold object gains energy through the process of heating from a hot object. We can summarize this relation as follows: © 2014 Pearson Education, Inc.

Tip © 2014 Pearson Education, Inc.

Effect of a moving piston on the temperature of an enclosed gas The particles collide with the moving piston. –When the piston is expanding, the particles move more slowly after the collision. –When the piston is compressing, the particles move more quickly after the collision. © 2014 Pearson Education, Inc.

Analyzing gas processes © 2014 Pearson Education, Inc.

Analyzing gas processes © 2014 Pearson Education, Inc.

Analyzing gas processes © 2014 Pearson Education, Inc.

Analyzing gas processes © 2014 Pearson Education, Inc.

Skills for solving gas problems using the first law of thermodynamics In addition to the standard problem-solving strategy, when doing the "simplify and diagram" step: –Decide whether you can model the system as an ideal gas. –Decide whether the gas undergoes one of the iso-processes. When doing the "mathematical representation" step: –Use a work-heating-energy bar chart to help apply the first law of thermodynamics. © 2014 Pearson Education, Inc.

Changing state The transformation of ice into water is a phase change—a process during which a substance changes from one state to another. Let's consider an experiment involving the heating of water that starts as very cold solid ice. © 2014 Pearson Education, Inc.

Melting and freezing At 0 °C, the phase change graph becomes vertical. The ice starts to melt but the thermometer reading does not change, even though energy is being added to the system. © 2014 Pearson Education, Inc.

Melting and freezing When we transfer energy to the solid material at the melting temperature, all of this energy goes into changing the potential energy of particle interactions, not the kinetic energy—thus the temperature does not change. © 2014 Pearson Education, Inc.

Energy to melt or freeze: Latent heat of fusion © 2014 Pearson Education, Inc.

Tip © 2014 Pearson Education, Inc.

Boiling and condensation The temperature of the water remains at the boiling temperature until all of the liquid water boils into vapor. Energy has been added to the water, but its temperature does not change. © 2014 Pearson Education, Inc.

Boiling and condensation For a molecule to leave the surface of a liquid, it must have enough kinetic energy to break away from the neighboring molecules, which are exerting attractive forces on it. The energy transferred to the liquid leads to a change in the potential energy component of the internal energy. © 2014 Pearson Education, Inc.

Energy to boil or condense: Heat of vaporization © 2014 Pearson Education, Inc.

Heats of fusion and vaporization © 2014 Pearson Education, Inc.

Things to notice about melting and boiling The values for the heats of fusion and vaporization are much larger than the specific heat. Much more energy is needed to change the state of a substance than to change its temperature. The values for heat of vaporization are significantly larger than the values for heat of fusion. More energy is required to boil the same mass of the same substance than to melt it. © 2014 Pearson Education, Inc.

Heating mechanisms How can we reduce energy losses from our homes during the winter? Why is the "dry heat" in Arizona less uncomfortable than a hot, humid day in Mississippi? Why should we be concerned about climate change? These questions are related to energy transfer mechanisms and, in particular, to the rate at which these transfers occur. © 2014 Pearson Education, Inc.

Conduction The process by which thermal energy is transferred through physical contact is called conductive heating or cooling. A quantity called thermal conductivity K characterizes the rate at which a particular material transfers thermal energy. –You want to use a material with low thermal conductivity to make a cup for holding hot beverages. © 2014 Pearson Education, Inc.

Thermal conductivity of materials (at 25 °C) © 2014 Pearson Education, Inc.

Conductive heating/cooling © 2014 Pearson Education, Inc.

Evaporation When gaseous water vapor is converted to liquid water (condenses), energy is released and returned to the object on which the vapor condenses, raising its temperature. To stay cool, you want the rate of evaporation to be somewhat greater than the rate of condensation. © 2014 Pearson Education, Inc.

Evaporative heating/cooling © 2014 Pearson Education, Inc.

Observational experiments © 2014 Pearson Education, Inc. Qualitatively Describe the Experiment

Observational experiments © 2014 Pearson Education, Inc.

Observational experiments © 2014 Pearson Education, Inc. Qualitatively Describe the Experiment

Observational experiments © 2014 Pearson Education, Inc.

Natural convective heating/cooling © 2014 Pearson Education, Inc.

Forced convective heating/cooling Thermal energy is transmitted by conduction to a coolant in a car's engine. The energy is then carried away by the fluid through a radiator hose and back to the radiator, where outside air moves past it and cools the fluid again. © 2014 Pearson Education, Inc.

Forced convective heating/cooling © 2014 Pearson Education, Inc.

Radiative heating/cooling © 2014 Pearson Education, Inc.

The greenhouse effect and climate change © 2014 Pearson Education, Inc.

Work, heating, and energy changes in the body of a runner © 2014 Pearson Education, Inc.

Summary © 2014 Pearson Education, Inc.

Summary © 2014 Pearson Education, Inc.

Summary © 2014 Pearson Education, Inc.

Summary © 2014 Pearson Education, Inc.