E. Calorimetry

q = m • C • T

q = heat or enthalpy J

m = mass g

C = specific heat J/g°C

T = temperature change °C

Note – these problems could also be done in calories

qsys = - qsurr

Tm

q

(C)Heat Specificor Capacity Heat Specific

Tells how much heat is required to change the temp of a substance.

Some specific heats are

Al 0.902 J/g oC

Cu 0.385 J/g oC

H2O 4.184 J/g oC

 

Quantity of heat supplied

Temperature change (always Tf-Ti)

• A 55.0 g piece of metal was heated in boiling water to a temperature of 99.8oC and dropped into an insulated beaker with 225 mL of water (d = 1.00 g/ml) at 21.0 oC. The final temperature of the metal and water is 23.1oC. Calculate the specific heat of the metal assuming that no heat was lost to the surroundings.

1. Pressure Constant (Coffee Cup)

Calculate Hrxn in kJ/mol when mixing:

50 mL of 0.10M AgNO3

50 mL of 0.10M HCl in a coffee cup calorimeter. The temperature rises from 22.3 °C to 23.1 °C.

AgNO3(aq) + HCl(aq) AgCl(aq) + HNO3(aq)

2. Volume Constant (Bomb Calorimeter)

qrxn = - Cbomb • T

Cbomb is anexperimentallydetermined valueusing a knownmaterial.

Each calorimeter hasits own constant value!!

2. Volume Constant (Bomb Calorimeter)

• Octane, C8H18, a primary constituent of gasoline, burns in air.

2 C8H18(l) + 25 O2(g) 16 CO2(g) + 18 H2O(l)

• Suppose that a 1.00 g sample of octane is burned in a calorimeter that contains 1.20 kg of water. The temperature of the water and the bomb rises from 25.00oC to 33.20oC. If the specific heat of the bomb, Cbomb, is known to be 837 J/oC, calculate the molar heat of reaction of C8H18.