By the end of this section, you will be able to: * Define energy, distinguish types of energy, and describe the nature of energy changes that accompany chemical and physical changes We burn a variety of fuels to produce energy for transportation, heating, and the generation of electricity.
Industrial chemical reactions use a lot of energy.
The raw materials are used to make useful products, such as cars, skyscrapers, and bridges.
A cheeseburger for lunch provides the energy you need to get through the rest of the day, while the combustion of gasoline provides the energy that moves your car between home, work, and school.
The majority of the energy we use comes from the sun.
The sun provides the earth with almost 10,000 times the amount of energy needed to meet all of the world's energy needs.
Our challenge is to find ways to convert and store incoming solar energy so that it can be used in chemical processes that are both convenient and nonpolluting.
Plants andbacteria take in the sun's energy.
When we burn wood or plant products, the energy stored in plants is released.
This energy is used to fuel our bodies by eating food that comes from plants or animals that get their energy from eating plants.
Burning fossil fuels releases stored solar energy.
Almost all scientific and technical fields use the concepts introduced in this chapter.
They are used to determine the energy content of food.
The metabolism of sugar into carbon dioxide and water is studied by biologists.
The oil, gas, and transportation industries, renewable energy providers, and many others are trying to find better ways to produce energy for our commercial and personal needs.
Engineers strive to improve energy efficiency, find better ways to heat and cool our homes, and meet the energy and cooling needs of computers and electronics, among other applications.
The OpenStax book is free for anyone who studies or does any kind of science.
When we inflate a bicycle tire, we move the air in the pump against the air already in the tire.
There are different types of energy.
Water at the top of a waterfall has potential energy because of its position, and when it flows downward through generators, it has energy that can be used to do work and produce electricity in a hydroelectric plant.
The chemicals in the battery can produce electricity that can work.
The water's potential energy is converted into energy when it falls.
During a chemical or physical change, energy can be neither created nor destroyed, although it can be changed in form.
There is always an associated conversion of one form of energy into another when one substance is converted into another.
Light, electrical energy, or some other form of energy can be used to convert heat into something else.
Potential energy is stored in the molecule that composes gasoline.
When gasoline is combusted within the cylinders of a car's engine, the rapidly expanding gaseous products of this chemical reaction generate mechanical energy.
There is no change in the total amount of matter during a chemical change.
When chemical reactions occur, the energy changes are relatively modest and the mass changes are too small to measure, so the laws of energy and matter hold well.
In nuclear reactions, the energy changes are much larger, the mass changes are measurable, and matter-energy conversions are significant.
The universe has a fixed quantity of matter and energy.
The object is cold when the atoms and molecules are moving slowly.
Increasing the amount of thermal energy in a sample of matter will cause its temperature to increase if there is no chemical reaction or phase change.
The amount of thermal energy in a sample of matter will decrease if there is no chemical reaction or phase change.
Click here to see the effects of temperature on motion.
As their temperature increases, most substances expand.
The operation of many thermometers depends on the expansion and contraction of substances in response to temperature changes.
When heated or cooled, one of the metals expands or contracts more than the other, causing the strip to coil or uncoil.
Both types of thermometers have a scale that shows the temperature.
The effects of heating and cooling a coiled bimetallic strip are shown.
A redundant term, heat flow increases the thermal energy of one body and decreases the thermal energy of the other.
Suppose we have a high temperature and a low temperature substance.
If we place substance H in contact with substance L, the thermal energy will flow from substance H to substance L.
The temperature of substance H will decrease, while the temperature of substance L will increase.
To explore energy forms and changes, click on the simulation.
To create combinations of energy sources, transformation methods, and outputs, visit the Energy Systems tab.
To see the transfer of energy, click on Energy Symbols.
Matter undergoing chemical reactions can release heat.
An example of an endothermic process can be found in a cold pack used to treat muscle strains.
The process of absorbing heat when water and a salt are brought together leads to the sensation of cold.
The metal being cut is melted by the exothermic reaction.
The molten metal has small sparks flying away.
The amount of energy required to raise one gram of water is called a calor.
The starting temperature of the water and the atmospheric pressure determine this quantity.
The easiest way to measure energy changes in calories is still being used.
The kilocalorie is the large calories used in quantifying food energy content.
The joule is the SI unit of heat, work, and energy.
James Joule was an English physicist.
1 newton-meter is the equivalent of 1 joule.
1000 joules is a kilojoule.
The definition has been set to 4.184 joules.
Two concepts have been introduced to describe heat flow and temperature change.
The amount of substance that absorbs or releases heat is what determines heat capacity.
It is an extensive property because it is proportional to the amount of the substance.
Consider the heat capacities of two frying pans.
The heat capacity of the large pan is five times greater than that of the small pan because the mass of the large pan is five times greater than the mass of the small pan.
It takes more energy to make the larger pan vibrate because more atoms are present in it.
The larger cast iron frying pan requires 90,700 J of energy to raise its temperature by 50.0 degrees.
The kind of substance absorbing or releasing heat is the only thing that matters.
It is an intensive property, but not the amount of the substance.
Although the large pan is larger than the small pan, they both yield the same value for specific heat.
Specific heat is measured in units of energy per temperature per mass and is an intensive property, being derived from a ratio of two extensive properties.
The heat capacity per mole is an intensive property.
A large frying pan has a larger heat capacity than a small frying pan.
The frying pans have the same heat because they are made of the same material.
The heat of a substance varies with the temperature.
Specific heat will be treated as constant over the range of temperatures that will be considered in this chapter.
Table 5.1 contains specific heats of some substances.
The temperature of the water in the flask increases from 21 degrees to 85 degrees.
Consider these factors when answering the question: the specific heat of the substance being heated, the amount of substance being heated, and the magnitude of the temperature change.
To heat 1 g of water by 1 degree requires a specific heat of 4.184 J.
The iron has a specific heat of 0.451 J/g.
If the other three are known or can be deduced, the relationship between heat, specific heat, mass, and temperature change can be used to determine any of these quantities.
The temperature of the metal piece increases when it absorbs 6.64 kJ of heat.
Determine the specific heat of this metal, which might give a clue to its identity.
This value matches the specific heat of aluminum, which suggests that the unknown metal may be aluminum.
The temperature of a piece of metal increases when it absorbs heat.
Predict the identity of this metal by determining its specific heat.
The sun's rays contain thousands of times more energy than we capture.
Solar thermal systems can be used to convert energy from the sun into energy we can use.
Large-scale solar thermal plants have different design specifics, but all concentrate sunlight to This OpenStax book is available for free.
The Solana Generating Station is located in Arizona's Sonora Desert.
It uses mirrors that focus sunlight on pipes.
It turns water into steam, which spins a turbine, which in turn produces electricity, and it also heats a mixture of salts, which is used as a thermal energy storage system.
After the sun goes down, the molten salt mixture can release enough of its stored heat to produce steam to run the turbine for 6 hours.
High heat capacities and thermal conductivities are some of the beneficial properties of molten salts.
The solar thermal plant uses mirrors to concentrate sunlight.
Its 170,000 mirrors focus huge amounts of sunlight on three water-filled towers, which produce steam over 538 degC.
It can power 140,000 homes.
Water has a large heat capacity and can be used as a working fluid.