When matter gets warmer, the atoms or molecules in the matter move faster.
All matter-solid, liquid, and gas-is composed of continually jiggling atoms or molecules. Because of this random motion, the atoms and molecules in matter have kinetic energy. The average kinetic energy of these individual particles causes an effect we can sense-warmth.
Whenever something becomes warmer, the kinetic energy of its atoms or molecules has increased. When the atoms or molecules in matter move faster, the matter gets warmer. Its atoms or molecules have more kinetic energy.
The higher the temperature of a substance, the faster is the motion of its molecules.
The quantity that tells how hot or cold something is compared with a standard is temperature. Nearly all matter expands when its temperature increases and contracts when its temperature decreases.
Celsius Scale
The most widely used temperature scale is the Celsius scale.
•The number 0 is the aat which water freezes.
•The number 100 is the temperature at which water boils.
The gap between freezing and boiling is divided into 100 equal parts, called degrees
Fahrenheit Scale
The temperature scale used commonly in the United States is the Fahrenheit scale.
•The number 32 is the temperature at which water freezes.
•The number 212 is the temperature at which water boils.
•The Fahrenheit scale will become obsolete if and when the United States goes metric.
Kelvin Scale
Scientific research uses the SI scale-the Kelvin scale.
•Degrees are the same size as the Celsius degree and are called “kelvins.”
•On the Kelvin scale, the number 0 is assigned to the lowest possible temperature-absolute zero.
•At absolute zero a substance has no kinetic energy to give up.
•Zero on the Kelvin scale corresponds to -273°C.
Scale Conversion
Arithmetic formulas can be used for converting from one temperature scale to another.
In the simplest case of an ideal gas, temperature is proportional to the average kinetic energy of molecular translational motion.
The warmth you feel when you touch a hot surface is the kinetic energy transferred by molecules in the surface to molecules in your fingers.
Temperature is not a measure of the total kinetic energy of all the molecules in a substance.
Two liters of boiling water have twice as much kinetic energy as one liter.
The temperatures are the same because the average kinetic energy of molecules in each is the same.
When two substances of different temperatures are in thermal contact, heat flows from the higher-temperature substance into the lower-temperature substance.
If you touch a hot stove, energy enters your hand from the stove because the stove is warmer than your hand.
If you touch ice, energy passes from your hand into the colder ice.
The direction of spontaneous energy transfer is always from a warmer to a cooler substance.
The energy that transfers from one object to another because of a temperature difference between them is called heat.
Matter contains energy but it does not contain heat. Heat is energy in transit, moving from a body of higher temperature to one of lower temperature.
When heat flows from one object or substance to another it is in contact with, the objects are said to be in thermal contact.
Heat flows according to temperature differences-that is, average molecular kinetic energy differences.
Heat never flows on its own from a cooler substance into a hotter substance.
When a thermometer is in contact with a substance, heat flows between them until they have the same temperature.
After objects in thermal contact with each other reach the same temperature, we say the objects are in thermal equilibrium. When objects are in thermal equilibrium, no heat flows between them.
To read a thermometer we wait until it reaches thermal equilibrium with the substance being measured. The temperature of the thermometer is also the temperature of the substance.
When a substance takes in or gives off heat, its internal energy changes.
In addition to the translational kinetic energy of jostling molecules in a substance, there is energy in other forms.
•There is rotational kinetic energy of molecules.
•There is kinetic energy due to internal movements of atoms within molecules.
•There is potential energy due to the forces between molecules.
•The total of all energies inside a substance is called internal energy. A substance contains internal energy, not heat.
Absorbed heat may make the molecules of a substance jostle faster. In some cases, as when ice is melting, a substance absorbs heat without an increase in temperature. The substance then changes phase.
The amount of heat transferred can be determined by measuring the temperature change of a known mass of a substance that absorbs the heat.
Heat is energy transferred from one substance to another by a temperature difference.When a substance absorbs heat, the resulting temperature change depends on more than just the mass of the substance.
The most commonly used unit for heat is the calorie.
The calorie is defined as the amount of heat required to raise the temperature of 1 gram of water by 1°C.
The kilocalorie is 1000 calories (the heat required to raise the temperature of 1 kilogram of water by 1°C).
The heat unit used in rating foods is actually a kilocalorie, although it’s often referred to as the calorie.
To distinguish it from the smaller calorie, the food unit is sometimes called a Calorie (written with a capital C).
The calorie and the Calorie are units of energy. In the International System of Units (SI), quantity of heat is measured in joules, the SI unit for all forms of energy.
One calorie equals 4.186 J.
The capacity of a substance to store heat depends on its chemical composition.
A material requires a specific amount of heat to raise the temperature of a given mass a specified number of degrees.
The specific heat capacity of a material is the quantity of heat required to raise the temperature of 1 gram by 1 degree.
