Lecture 1 2024-2025 Heat and Thermodynamics PDF

1 Heat and Thermodynamics First Science 2024 – 2025 A. prof. Dr. Ashraf Mahmoud  The concept of heat and temperature Some people think that temperature and heat are the same, but they are not. They are rather related to each other but not the same....

1 Heat and Thermodynamics First Science 2024 – 2025 A. prof. Dr. Ashraf Mahmoud  The concept of heat and temperature Some people think that temperature and heat are the same, but they are not. They are rather related to each other but not the same. Temperature () 1- Temperature is not energy, but a measure the average kinetic energy of the disordered motion of atoms and molecules of a substance. 2-Temperature is the measure of coldness or hotness. Thermometer is an instrument that is used to measure temperature It contains a thermometric substance, measuring a substance, like mercury, whose physical property changes with change in temperature.  K.E    k  T 3 2 If the temperature is measured in degrees Kelvin. Then the temperature value is directly proportional to the average of kinetic energy of the molecules in the substance being measured.  Temperature scales (1) There are upper fixed and lower fixed points. The upper fixed point is steam point and is the temperature at which steam forms from pure water, boiling at normal atmospheric pressure. The lower fixed point is the temperature of mixture of ice and water at normal atmospheric pressure. The Fahrenheit and Celsius are more commonly used temperatures scales The Celsius scale, has the upper fixed point or steam point at 1000 and the low fixed point ore ice point of 00 which mean that the boiling point of water in the Celsius scale is 100 0C and the freezing point of water is 0 0C. There are 100 equal divisions between 00 and 1000, such that each division is one degree Celsius (10C). The Fahrenheit scale, has the upper fixed point or steam point at 2120 and the low fixed point ore ice point of 320 which mean that the boiling point of water in the Fahrenheit scale is 2120 and the freezing point of water are 320. There are 180 equal divisions between 320 and 2120, such that each division is one degree Fahrenheit (10F). Kelvin scale temperature are measured in degrees, the same size as degree Celsius. The scale does not have negative values. 0 K, is the same as -273 0C. The freezing point (ice point) of water in the Kelvin scale is 273 K and 373 K is the boiling point (steam point) of water. The Celsius and Kelvin scales are related as shown below. K = C + 273 Cooling substances gradually immobilize molecules and reduce their kinetic energy unit they are theoretically depleted of kinetic energy. This occurs at -2730C, also called absolute zero.  Conversion between temperatures   C  0  F  32  K  273  100  180    100  1) 80 0F = …. 0C.   C  0  F  32    100 180    C  80  32    180   C  100  80  32  100 180   C  26.7 0C 2) 80 0C = …. 0F.  80  F  32    100 180   80  F  32    80 180  100   F  32  100 180  14400  100   F  3200 17600  100   F  F  1760F What is the value of the freezing point of oxygen gas on the Celsius scale if its value is -362 0F    0  F  32  C   100 180      362  32  C   180   C  100   362  32  100 180   C  218.9 0 C The temperature of absolute zero on the Celsius scale is -273 0C, what is its value on the Fahrenheit scale?   273  F  32     49140  100 F  3200  100 180   49140  3200  100 F  45940  100 F  F  459.40F  At what temperature do the readings of the Fahrenheit and Celsius scales agree, and what is the temperature whose value on the Celsius scale is twice its value on the Fahrenheit scale?   C   F  32    100 180       32  C   F      100 180  180    100    3200 80    3200    40 0 C   C   F  40 0 C    80  F  32  C  2 F  C  80 C  0   100 180   14400  100   F  3200  11200  100   F  F  1120 F  Temperature Scales (2) we can define the temperature in the mercury-in-glass scale by  L  L0       100  L100  L0  0 C We could define a platinum resistance temperature scale by  R  R0       100  R100  R0  0 C We could define a thermoelectric temperature scale by  V  V0       100  V100  V0  0 C We could define a constant volume gas temperature scale by  P  P0      100  P100  P0  0 C A platinum resistance thermometer whose resistance is at zero degrees Celsius7.395, in degrees100 0C, 8.965, so if its resistance is in the middle of what it is 8 Then the temperature of the medium is  R  R0   0 C     100  R100  R0   8  7.395   0 C    100  38.5 C 0  8.965  7.395  A constant pressure air thermometer gave a reading of 47.5 units of volume, when immersed in ice-cold water, and 67 units in a boiling liquid. What is the boiling point of the liquid?  V  V0   0 C     100  V100  V0   67  47.5      100  100 C 0  67  47.5  0 C