Solving Heat (calorimetry) transfer problems

1
Solving Heat (calorimetry) transfer problems

• Finding the amount of heat to raise or lower the
  temp of a substance

2
Heat Problems

• Q mc(Tf-Ti) Heat required to change the
  temperature of a material. c specific heat and
  m mass (kg)
• Q heat, measured in joules
• C(water) 4186 J/kg k
• C(ice) 2090 J/kg k
• C (aluminum) 900 J/kg k.

3
Heat Problems

• When a material goes through a phase change
  (melting from solid to liquid, or boiling from
  liquid to gas) the amount of heat energy required
  is called the Latent heat.
• L latent heat
• L(melting water) 334,000 J/kg
• L(boiling water) 2,257,000 J/kg
• Q mL heat required for a phase change

4
Heat problems

• Calculate the heat required to raise 2kg of water
  and aluminum from 25C to 60C
• Q mc (Tf-Ti)
• Q(water) (2kg) (4186 J/kg k) (60-25) 293000J
• Q(alum) (2kg) (900 J/kg k) (60-25) 63,000J

5
Heat Problems

• Calculate the heat required to bring 2 kg of ice
  at -20C to water at 5C
• Q Q(heat ice from -20C to 0C) Q (melt the ice
  to water) Q(heat water from 0 to 5C)
• Q mc(ice)(0- -20C) mL(melting) mc(water) (5
  0C)
• Q 2kg(2090)(20C) 2kg(334000J/kg k)
  2kg(4186)(5C) 793460J