Thermodynamics Part 1: Work, Heat, Internal Energy and Enthalpy
Thermodynamics Part 1: Work, Heat, Internal Energy and Enthalpy Energy - The potential energy stored in the electrostatic bonding relationships among. Scientists define heat as thermal energy transferred between two systems at different temperatures that come in contact. Relationship between heat and temperature This is why chemists can use the melting point to help identify a pure substance − - −the temperature at .. Calculating internal energy and work example. Calculating the Amount of Work Done by Forces · Potential Energy · Kinetic Energy · Mechanical Energy · Power. Lesson 2 - The Work-Energy Relationship.
Note that removal of heat implies a negative q value, and that for proper dimensional analysis, q must be expressed in J. The final temperature is found according to the relationship: Supposing that all three are intially at a room temperature of Suppose now that a g block of iron heated to In accordance with the first law: If the system is perfectly insulated, the two blocks would remain at Tf for eternity.
By substituting the heat capacity formula, we can solve for this equilibrium temperature: Two isolated metal blocks under the given conditions would come to an equilbrium temperature of Schematic Diagram of a Bomb Calorimeter Naphthalene is a hydrocarbon often used in moth balls Calorimetry The science of calorimetry is used to determine the heat energy or caloric content of a material in familiar applications, the energy content of foods.
Using a device called a bomb calorimeter, a sample is placed in a chamber known as a bomb of known heat capacity which is immersed in water. The water bath is insulated to prevent heat loss to the outside. Oxygen is pumped into the chamber, and a spark is used to ignite the sample. After complete combustion, the temperature inside the calorimeter reaches a maximum and this can be used to compute the heat energy content of the sample.
Traditionally, the calorie energy unit is used and is defined to be the amount of energy required to raise one gram of water one degree Celsius. Considering the calorimeter as an isolated system, the heat content of a sample burned in the bomb can be found from: The calorimeter chamber is filled with g of water and the initial temperature is measured at The bomb is ignited and the final temperature inside the calorimeter rises to a maximum of The heat content of the combustion reaction is found to be: Note that the combustion reaction is exothermic.
Using a molar mass of Applications of calorimetry in the determination of food energy content use the Food Calorie unit: Conversely, energy can be used to induce net movement, or do work on a system.
Electrons moving through a potential, coiling or releasing a spring, and squeezing fluids hydraulic action are examples of processes which can either produce or require work. We will examine a fourth type of work in this lesson; that which results in expansion or contraction of a gas against an external resistance called PV-work.
Some clarification on the above notation may be helpful. The external pressure is applied to a gas sample as an opposing force to its internal pressure.
In many instances Pext is supplied by the atmosphere, for instance as it resists the evolution of a H2O g from H2O l in evaporation. A more instructive example is given by the example to the left, a gas confined within a cylinder by a sliding piston.
The piston moves inward, increasing internal pressure until the two pressures match. In this case we say that work is done on the gas.
Heat and temperature
Unit analysis of the pressure-volume product shows that it has the same dimensions as energy: Volume behaves as a state function. Independent of any or all intermediate steps, the change in volume only depends on the initial and final readings. Like other thermodynamic variables, internal energy exhibits two important properties: Being a state function means that E has the following property: Take as an example measuring volume changes.
However the change in volume each time will be exactly the same no matter how many intermediate steps are taken. It is quite remarkable how much of chemistry is measured in a relative sense, that is, as a difference between two absolute values.
Work, Energy, and Power
The significance of state functions in difference measurements is profound. The thermal energy will flow in that direction until the two objects are at the same temperature. When the two systems in contact are at the same temperature, we say they are in thermal equilibrium.
Zeroth law of thermodynamics: Defining thermal equilibrium The zeroth law of thermodynamics defines thermal equilibrium within an isolated system. The zeroth law says when two objects at thermal equilibrium are in contact, there is no net heat transfer between the objects; therefore, they are the same temperature.
Another way to state the zeroth law is to say that if two objects are both separately in thermal equilibrium with a third object, then they are in thermal equilibrium with each other. The zeroth law allows us to measure the temperature of objects.
Internal Energy, Heat, and Work
Any time we use a thermometer, we are using the zeroth law of thermodynamics. For a spring this can be written: The larger k is, the stiffer the spring is and the harder the spring is to stretch. If an object applies a force to a spring, the spring applies an equal and opposite force to the object. This is a restoring force, because when the spring is stretched, the force exerted by by the spring is opposite to the direction it is stretched.Relation Between Internal Energy Work And Heat
This accounts for the oscillating motion of a mass on a spring. If a mass hanging down from a spring is pulled down and let go, the spring exerts an upward force on the mass, moving it back to the equilibrium position, and then beyond.
This compresses the spring, so the spring exerts a downward force on the mass, stopping it, and then moving it back to the equilibrium and beyond, at which point the cycle repeats.
This kind of motion is known as simple harmonic motion, which we'll come back to later in the course. The potential energy stored in a spring is given by: In a perfect spring, no energy is lost; the energy is simply transferred back and forth between the kinetic energy of the mass on the spring and the potential energy of the spring gravitational PE might be involved, too.
Conservation of energy We'll take all of the different kinds of energy we know about, and even all the other ones we don't, and relate them through one of the fundamental laws of the universe.
The law of conservation of energy states that energy can not be created or destroyed, it can merely be changed from one form of energy to another. Energy often ends up as heat, which is thermal energy kinetic energy, really of atoms and molecules. Kinetic friction, for example, generally turns energy into heat, and although we associate kinetic friction with energy loss, it really is just a way of transforming kinetic energy into thermal energy.
The law of conservation of energy applies always, everywhere, in any situation.