Describe the following terms:
b) latent heat
e) spontaneous combustion
f) enthalpy of evaporation of steam
g) British thermal unit (BTU)
A) SPECIFIC HEAT:
The specific heat of a substance is the quality of heat required to raise the temp of a unit mass
of a substance by one degree. Water is used as the standard substance because it has a greater
capacity for heat than any other known liquid, as well as most solids. Gases have two different
specific heats according to whether heat is applied at constant volume or constant pressure.
Specific heat is measured in British Thermal Unit or BTU.
B) LATENT HEAT
Latent heat is the heat which supplies the energy necessary to overcome the bending forces of
attraction between the molecules of a substance, and is responsible for it changing its physical
state from a solid into a liquid or from a liquid into a vapor the change taking place without any
change in temperature.
C) CALORIFIC VALUE:
The heat energy given off during complete combustion of unit mass of fuel in the cylinders of an
internal combustion engine is termed the calorific value and may be expressed of kilojoules of
heat energy given during the burning of one kilogram of fuel.
Temperature is the degree of hotness or coldness of a body relative to some zero value. Is a
measure of intensity of heat? The fact that one body has a higher temp than the other does not
mean that the hotter body necessarily contains more heat. Heat will always flow from a hotter
body to a colder body in contact with it, however this does not mean that a rise in temperature
of the colder body will equal to the fall in the temp of the hotter body even through the mass in
each case is equal and the transfer takes place without loss.
E) SPONTANEOUS COMBUSTION:
Spontaneous combustion refers to a material bursting into flame without being ignited by an
outside source (sparks or flame). Ignition often occurs through the chemical interaction of two
or more substances, one of which is often air or water. Sodium and potassium react with water.
Magnesium, titanium, calcium, and zirconium oxide rapidly in the presence of air. Careful
storage of materials is an ever present fact in the prevention of fire by spontaneous combustion.
F) ENTHALPY OF EVAPORATION OF STEAM:
Enthalpy of evaporation of steam is equal to the latent heat of evaporation. the process of
changing the physical state of a substance from a liquid into a vapor is called boiling or
evaporation, and the quantity of heat to bring about change at a constant temp to unit mass is
the latent heat of evaporation.
G) BRITISH THERMAL UNIT:
British thermal unit refers to the quantity of heat in one degree, the temperature of the water
being that of maximum density namely 39.2 F