Potential energy + kinetic energy = internal energy
Total internal energy of all the molecules of a substance is called thermal energy
Energy which flows from hot body to cold body is called heat energy/heat
Heat: form of energy which flows from a hot body to a cold body when they are kept in contact
Calorimetry: measurement of quantity of heat
SI unit of heat - joule
One calorie is the quantity of heat energy required to raise the temperature of 1g of water from 14.5C to 15.5C
2 cal = 4.186 J(or nearly 4.2 J)
1 kcal = 1000 J = 4200 J(nearly)
One kilo-calorie is the heat energy required to raise the temperature of 1 kg of water from 14.5C to 15.5C
Kcal - energy value of food
Temperature determines the direction of flow of heat for bodies in contact
Temperature: a parameter which tells the thermal state of a body(degree of hotness or coldness of body). It determines the direction of flow of heat when two bodies of different temperatures are placed in contact
If there is no transfer of heat between two bodies placed in contact, they are said to be at the same temperature, but doesn’t meant that they have the same amount of thermal energy
SI unit of temperature = Kelvin
TK = 273 + t C(t: temperature)
By adding 273.15 to the temperature in degree celsius, we get the temperature in kelvin
Change in T C = Change in T K
Factors affecting quantity of heat absorbed to increase the temperature of a body:
- Mass
Objects with different mass made from the same substance absorb different amounts of heat energy to raise their temperature by the same amount
- Increase in temperature
Objects with equal mass made from the same substance absorb different amounts of heat energy to raise their temperature by different amounts
- Material/substance of body
Objects of same mass but made from different substances absorb different amounts of heat energy to raise their temperatures by the same temperature
Heat:
- Amount of heat contained in a body depends on mass, temperature and substance
- Measured by calorimetry
- Two bodies with same temperatures may have different temperatures
- When two bodies are placed in contact, the total amt of heat is equal to the sum of the heats of the individual bodies
Temperature:
- Temperature of a body depends on average kinetic energy of molecules due to random motion
- Measured by thermometer
- Two bodies with same temperature may have different heat
- When two bodies of different temperatures are kept in contact, the resultant temperature is in between the two temperatures
Heat capacity: amount of heat energy required to raise its temp by 1C
C’ = Amount of heat supplied/change in temperature
C’ = Q/Δ t
Q = c m Δ t(c = constant of proportionality called specific heat capacity)
SI unit of heat capacity: J K^-1 or J C^-1
Specific heat capacity of a substance is defined as the heat capacity per unit mass of a body of that substance
Specific heat capacity c = C’/m
C = Q / m x Δ t
Specific heat capacity of a substance is the amt of heat energy required to raise the temperature of unit mass of the substance through 1C or 1K
c = amt of heat supplied/mass x rise in temperature
C’ = m x specific heat capacity
Good conductor of heat - low c
Calorimeter - cylindrical vessel used to measure amt of heat gained/lost by a body when mixed with another body/substance
- Made of copper
- Good conductor - vessel soon acquires temperature of its contents
- Low specific heat capacity
- Inner surfaces polished to reduce loss of heat due to radiation
- Placed inside wooden jacket for insulation
- Space between calorimeter and jacket filled with poor conductor
- Covered with wooden lid to avoid loss of heat through convection
- Two holes for stirrer and thermometer
Principle of calorimetry: Heat energy by lost body = heat gained by cold body
M1 * c1 * (t1 - 1) = m2 * c2 * (t - t2)
Natural phenomena and consequences of high specific heat capacity of water:
- Moderate seashore climate
- Hot water bottles used for fomentation
- Water is effective coolant
- Water is used to keep wine and juice from freezing
- Farmers fill their fields with water to prevent crops from frost