Class – 9 Chemistry

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Class – 9 Chemistry The common unit of Temperature :- The common unit of measuring temperature is degree Celsius which is written in short form as°C. There is another scale of temperature called Kelvin scale of temperature the SI unit of measuring temperature is Kelvin it is denoted by the symbol K . 0°C = 273 K The relation between Kelvin scale and Celsius scale of temperature can be written as Temperature of Kelvin scale = Temperature of Celsius scale+273 Example 1. convert the temperature of 25 °Cto the Kelvin scale. Solution :- Temperature on Kelvin scale = Temperature on Celsius scale + 273 =25+273 =298K Thus a temperature of 25 degree Celsius on Celsius scale is equal to 298 Kelvin on the Kelvin scale. Example 2 . Convert the temperature of 300 Kelvin to the Celsius scale. Solution. we know that temperature on Kelvin scale =Temperature on Celsius scale + 273 so , 300 = temperature on Celsius scale + 273 and , temperature on Celsius scale = 300 – 273 =27 degree Celsius Thus a temperature of 300 Kelvin on Kelvin scale is equal to 27 degree Celsius on Celsius scale. Note. It is clear from the above discussion that: 1. To convert a temperature on Celsius scale to the Kelvin scale we have to add 273 to the Celsius temperature. 2. and the convert a temperature on Kelvin scale to the Celsius scale we have to subtract 273 from the Kelvin temperature. Temperature is measured in Fahrenheit also. People in USA used the Fahrenheit degree while Indians use the Celsius degree. So we need to find out the exact temperature on means, if he says that he is at 100° F. If Fahrenheit is considered, then the boiling point of water is taken as 212° F and 32°F is the freezing point of water. We have the formula to deal with the conversion of Fahrenheit to Celsius degree. Formula to convert Fahrenheit to Celsius C=(F−32)×5/9 Formula to convert Celsius to Fahrenheit F=C×9/5+32 It is also known as Centigrade to Fahrenheit formula. Kelvin to Fahrenheit formula F=9/5(K–273)+32 The degree Fahrenheit is denoted as F° The relation between Fahrenheit and Celsius is 1° C = 1.8° F. Solved Examples Question 1: Convert Fahrenheit to Celsius: (a) 12° F (b) 22° F Solution: The Fahrenheit to Celsius is given by the formula C = (F – 32) × 5/9 (a) 12° F = (12 – 32) × 5/9 = – 11.11° C (b) 22° F = (22 – 32)x5/9=-5.55° C. Work sheet 1. Convert the temperature given in the Celsius scale to the Fahrenheit scale: (i) 25° C (ii) 45° C (iii) 0° C (iv) 20° C (v) 90° C (vi) 40.3° C (vii) 65° C 2. Convert the temperature given in the Fahrenheit scale to the Celsius scale: (i) 102° F (ii) 37° F (iii) 200° F (iv) 175° F (v) 185° F (vi) 158° F (vii) 68° F 3. Convert 278.15 Kelvin to Celsius scale. 4 . Convert 288.15 Kelvin to Celsius scale . 5. Convert 289.15 Kelvin to Celsius scale. 6. Convert 285.15 Kelvin to Celsius scale. 7. Convert 25 degree celsius to Kelvin scale. 8. Convert 298.15 Kelvin to Celsius scale. 9. Convert 277.15 Kelvin to Celsius scale. 10. Convert 286.15 Kelvin to Celsius scale. .

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