Energy in Thermal Processes

Heat

Calorimetry

Phase Changes

Heat and Internal Energy

• _______ _______, U, is energy of atoms and molecules of a system– Includes KE of translation, rotation, vibration– Includes PE of chemical/electrical bonds

• ______, Q, is transfer of energy between system and environment due to temperature difference ΔT

Units of Heat• Historically defined in terms of __________

_________ of object– calorie (cal) – the energy necessary to raise the

temperature of 1g of water from 14.5°C to 15.5°C

– British thermal unit (BTU) – the energy necessary to raise the temperature of 1 lb of water from 63°F to 64°F

• Heat (like work) is a transfer of energy and has SI units of ________

J 186.4cal 1

Specific Heat

• Every substance requires a ________ amount of energy per unit mass to change T by 1°C

• Characterize the material by its _______ heat c

• Units are J/(kg∙°C)

• See Table 11.1, p. 355

TmcQTm

Qc

2.11

if TTT

Calorimetry

• Use containers that are good ________ (no energy leaves/enters the container)

• Put warmer and cooler materials in container

• Apply conservation of ______ hotcold QQ

In general 0kQ

Sign of ____ takes care of sign of Q

Latent Heat and Phase Change• Sometimes energy transfer results in

changes of ____ (melting/freezing = _____, boiling/condensing = _________)

• _____________ does not change

• Characterized by latent heat L

• See Table 11.2, p. 360; units are J/kg

6.11mLQ

Use + if ______ energy, – sign if _______ energy

Example: Ice to Steam

Fig. 11.3, p. 361TmcQ ice

fmLQ

TmcQ water

vmLQ TmcQ steam