Properties of Heat and Temperature

Properties of Heat and Temperature Heat is the transfer of energy from one body to another due to the difference in temperature between the two. A hotter object placed next to a cooler object will always transfer heat from itself into the cooler object, until both objects are of equal temperature. For example, when we place ice cubes in hot water, the heat from the hot water transfers to the ice cubes. This transfer of heat energy will continue until equilibrium is reached between the hot water and the ice. Heat is a measure of the internal energy that has been absorbed or transferred from one body to another. It is not conserved; it can be either created or destroyed. There are two general ways that heating can occur: from a temperature difference, with energy moving from the region of higher temperature, and from an object gaining energy by way of an energy-form conversion. The SI unit of heat is the  joule. The metric unit of heat is called the calorie (cal), which is defined as the amount of heat required to raise the temperature of one gram of water from 14.5oC to 15.5oC. The English systems measure of heating is called the British thermal unit (Btu), which is the amount of heat needed to increase the temperature of 1 pound of water 1 degree Fahrenheit. Some examples of heat energy are: chemical energy from the foods is converted into heating our bodies; light from the sun is converted to heat as the suns rays warm the earths surface; energy from friction creates heat, like when we rub our hands; in light bulbs, electrical energy is converted into heat energy, etc. What is temperature? Temperature is a degree of hotness or coldness of a body. For example, a hot oven is said to have a high temperature, and the ice is said to have low temperature. Temperature is the measure of the average kinetic energy of the particles, atoms or molecules, making up a substance. Temperature can be measured using a thermometer. It is measured in degrees on the Fahrenheit, Celsius, and Kelvin scales. What is the relationship between heat and temperature? Heat and temperature is not the same thing, but there is a relationship between them. When heat is introduced to a certain substance, its molecules start moving faster and collide with one another, which produce more heat and the temperature of the substance goes up. This implies that heat introduced to a substance, changes the temperature of the body. This relationship between heat and temperature can be explained by a property called specific heat,  c, which is defined as the amount of heat needed to increase the temperature of 1 gram of a substance 1 degree Celsius. Where  Q  is the amount of heat needed,  m  is the mass of the material,  c  is the specific heat of the material, and ΔT  is the change in temperature. From the above equation, the amount of heat needed is proportional to the temperature change, which means more heat will be needed to raise the temperature of the cool water and less heat will be needed to raise the temperature of the warm tea. How are they different? Heat and temperature are most definitely linked one another, but they are not same. Heat is the measure based on total internal energy, internal kinetic energy and internal potential energy, of the molecules of an object, whereas temperature is a measure of the degree of hotness and coldness of an object, a measure that is based on the average molecular kinetic energy. Heat is measured in joules (J) or calories (cal.) and temperature is measured in degrees on the Fahrenheit, Celsius, and Kelvin scales. Heat is an extensive property, while temperature is an intensive property. Heat depends on mass or quantity of the substance, whereas temperature does not depend on the quantity of matter. For example, if the boiling temperature of water is 100 °C, it will remain the same whether we boil one liter or 50 liters of water. But the amount of heat generated when we boil 1 liter of water is less as compared to heat generated when 50 liters of water is boiled to 100 °C. What are the various properties of a substance that determine its heat capacity? The heat capacity is the quantity of heat needed to raise the temperature of a substance by one degree Celsius. It is a measure of how much heat the object must gain or lose to change its temperature by a given amount. The SI unit for heat capacity is J/K (joule per Kelvin). In the English system, its units are British thermal units per pound per degree Fahrenheit (Btu/oF). The heat capacity differs from substance to substance. The amount of substance is directly proportional to the heat capacity. This means the amount of a substance (mass) determines its heat capacity; the more quantity of a substance or the greater the mass, more heat it would gain or lose to change its temperature by 1C. For example, it would take more heat to warm the pitcher of water by 1C than to warm a cup of water by 1C. The heat capacity also depends on the nature or type of material of which the object is composed; different materials require different amounts of heat gain or heat loss to change their temperature by 1 °C, even if they have the same masses. For example, it takes 1 calorie of sunlight to warm 1g of water 1 °C, whereas, it only takes 0.2 calories to change the temperature of 1g of soil by 1C Heat capacity might depend on the temperature of the object or the atmospheric pressure. For a gas, heat capacity would depend on whether pressure was being held constant during the heat gain or loss, or whether the volume was held constant, or neither.