Lecture 16 - Heat and Calorimetry

heat

energy that is transferred from hot object to cold object due to the difference in temperature

specific heat

heat needed to increase temperature of 1 kg of a substance by 1 degree K or C

specific heat formula

Q = mc delta T

• Q = heat energy (J)

• m = mass (g)

• c = specific heat

• delta T = change in temp (c or K )

water and … have the highest specific heat

the human body

what is calorimetry

the measure of heat exchange between bodies

what is a calorimeter

thermally insulated vessel that measures the specific heat of a given substance

• drop hot object into water

• measure temperature change of water

m0c0 delta T0 =

m(w)c(w) delta T(w)

heat lost from object is equal to

heat gained by water

bomb calorimeter

measures thermal energy released when substance burns

• how caloric content of food is measured

fusion

melting = solid to liquid

vaporisation

liquid to gas

what is required for something to change state/phase

energy

what is Latent Heat of Fusion (LF)

when 1kg of material transforms from solid to liquid

what is Latent Heat of Vaporisation (LV)

when 1kg of material transforms from liquid to gas

energy required is proportional to

mass of substance

Q =

Lm

• L = latent heat of transformation

fusion + vaporisation on graph looks like

plateau of temperature but energy is increasing

how to tackle this question:

a cooling tower condenses 100 degree C water steam into water at 35 degrees C. How much energy must be removed from the steam if 2 × 10³ of water is involved.

step 1 = find heat removed to condense steam (100 degrees) into water (100 degrees)

• Q1 = L(v)ms

step 2 = food ahead removed to cool water from 100 degrees to 35 degrees

• Q2 = mc(Th - Tc)

step 3 = add prior step results