Calorimetry

Measurement of heat changes in physical or chemical processes Based on the law of conservation of energy Idea that heat released by the system is equal to the heat gained by the surroundings (equal magnitude opposite direction)

Calorimeter Closed container designed specifically for measuring heat change Reaction at Constant P DH = qrxn qsys = qwater + qcal + qrxn qsys = 0 qrxn = - (qwater) No heat enters or leaves! Isolated system

Calculating heat 𝑞=𝑚𝑐∆𝑇 Change in temperature 𝑇 𝑓 − 𝑇 𝑖 Unit: C Specific heat J/gC Heat Unit: J or kJ Mass Unit: g

Specific heat Amount of heat required to raise the temperature of one gram of the substance by one degree Celsius Unit: J/gC Intensive property unique to each substance & can be used to identify the substance

What can be said about the amount of heat needed to raise 1 gram of each substance 1 C? The lower the specific heat, the less energy is required to raise its temperature

Example 1 If the temperature of 56.6g of ethanol increases from 45.0°C to 80.0°C, how much heat has been absorbed by the ethanol? Specific heat of ethanol =2.44J/g°C

Example 2 A 4.00g sample of a substance was heated from 274K to 314K and absorbed 32J of heat, what is the specific heat of the substance?

Example 3 If 98000J of energy are added to 6200mL of water, at 14C, what will the final temperature of the water be? Specific heat of water is 4.184 J/g°C

Example 4 A 45.0g sample of metal is placed in boiling water until its temp. is 100.0 C. a calorimeter contains 100.0g of water at a temp of 24.4 C. the metal sample is removed from the boiling water and immediately placed in water in the calorimeter. The final temp of the metal and water in the calorimeter is 34.9 C. assuming that the calorimeter provides perfect insulation, what is the specific heat of the metal?

Example 5 240g of water (initially at 21C) are mixed with an unknown mass of ion (initially at 501C). When thermal equilibrium is reached, the system has a temperature of 42 C. find the mass if the iron. Specific heat of iron = 0.449 J/gC

Example 6 Determine the final temperature when a 25.0g piece of iron at 85.0C is placed into 75.0 grams of water at 20.0C.