CHEMISTRY GLOSSARY

specific heat    →   specifični toplinski kapacitet

Specific heat is the quantity of heat required to raise the temperature of one gram of a substance by one degree Celsius.

heat capacity    →   toplinski kapacitet

Heat capacity is defined in general as dQ/dT, where dQ is the amount of heat that must be added to a system to increase its temperature by a small amount dT. The heat capacity at a constant pressure is C_p = (∂H/∂T)_p; that at a constant volume is C_V = (∂E/∂T)_V, where H is enthalpy, E is internal energy, p is pressure, V is volume, and T is temperature. An upper case C normally indicates the molar heat capacity, while a lower case c is used for the specific (per unit mass) heat capacity.

thermal resistance    →   toplinski otpor

Heat always flows from a higher to a lower temperature level. The driving force for the heat flux lies in the temperature difference ΔT between two temperature levels. Analogous to Ohm’s law, the following holds:

where H = dQ/dt is heat flux, measured in watts, ΔT is temperature difference across the thermal resistance, measured in kelvin, and R_th is thermal resistance, measured in K/W.

For example, suppose there were two houses with walls of equal thickness; one is made of glass and the other of asbestos. On a cold day, heat would pass through the glass house much faster. The thermal restistance of asbestos is then higher than of glass.

If the thermal Ohm’s law is divided by the heat capacity C, Newton’s law of cooling is obtained:

where dT/dt is rate of cooling or heating, measured in K s^-1, and C is heat capacity, measured in J K^-1.

buffer capacity    →   puferski kapacitet

Buffer capacity is number of moles of a strong acid or a strong base needed to change pH of 1 dm³ of buffer solution for pH unit.

specific quantity    →   specifična veličina

Specific quantity is often convenient to express an extensive quantity (e.g., volume, enthalpy, heat capacity, etc.) as the actual value divided by mass. The resulting quantity is called specific volume, specific enthalpy, etc.

thermal conductivity    →   toplinska vodljivost

Thermal conductivity (Λ) is rate of heat flow divided by the area and by the temperature gradient.

thermal pollution    →   toplinsko zagađenje

Thermal pollution is the increase in temperature of natural waters resulting from the discharge to these waters of hot effluents from industrial and power plants. The higher temperatures reduce the concentration of dissolved oxygen.

specific weight    →   specifična težina

Specific weight (γ) is defined as the ratio between the weight of a mass element, Δm, and the volume, ΔV, occupied by that element. As density (average) is defined as the ratio of a mass element and its volume, specific weight is equal to:

where g is gravitational acceleration.

thermal expansion    →   toplinsko rastezanje

Thermal expansion is a change in dimensions of a material resulting from a change in temperature. All objects change size with changes in temperature. The change ΔL in any linear dimension L is given by

in which α is the thermal coefficient of linear expansion, L_o is the initial or reference dimension at temperature T_o (reference temperature) and ΔT is change in temperature which causes the change in dimension.

The change ΔV in the volume of a sample of solid or liquid is

Here γ is coefficient of volume expansion, V_o is the volume of the sample at temperature T_o and ΔV is the change in volume over the temperature range ΔT. With isotropic substances, the coefficient of volume expansion can be calculated from the coefficient of linear expansion: γ = 3α.

Glauber’s salt    →   Glauberova sol

Glauber’s salt is sodium sulphate decahydrate (Na₂SO₄·10H₂O). Loses water of hydration at 100 °C. Energy storage capacity is more than seven times that of water.