Section 5.3 Energy, Temperature Changes and Changes of State.

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Presentation transcript:

Section 5.3 Energy, Temperature Changes and Changes of State

In this section: a.heat transfer: specific heat capacity b.calculating temperature changes c.changes of state d.heating curves

HEAT: What happens to thermal (heat) energy? Three possibilities: Warms another object Causes a change of state Is used in an endothermic reaction

Heat is added to a substance; how much does its temperature increase?

Specific heat capacity: energy required to raise the temperature of a 1 g sample by 1 o C

Determining specific heat capacity Using the following data, determine the specific heat capacity of silver. q = 150 J m = 5.0 g Ag T final = °C T initial = 20.0 °C

Trends in specific heat capacity

Heat and Temperature: Key Equation

Calculating temperature change. Calculate the final temperature reached when 324 J of heat is added to a 24.5-g iron bar initially at 20.0 °C.

What happens to thermal (heat) energy? When objects of different temperature meet: Warmer object cools Cooler object warms Thermal energy is transferred q warmer = -q cooler specific heat x mass x  T = specific heat x mass x  T warmer object cooler object

Heat transfer between substances: Specific heats: Cu = J/g  o C Wood = 1.8 J/g  o C

Predicting Thermal Equilibrium: Conceptually Easy Example: If we mix 250 g H 2 O at 95 o C with 50 g H 2 O at 5 o C, what will the final temperature be?

HEAT: What happens to thermal (heat) energy? Three possibilities: Warms another object Causes a change of state Is used in an endothermic reaction

Thermal Energy and Phase Changes First: What happens? Heating Curve

Thermal Energy and Phase Changes

Warming: Molecules move more rapidly Kinetic Energy increases Temperature increases Melting/Boiling: Molecules do NOT move more rapidly Temperature remains constant Intermolecular bonds are broken Chemical potential energy (enthalpy) increases But what’s really happening?

Energy and Phase Changes: Quantitative Treatment Melting: Heat of Fusion (  H fus ) for Water: 333 J/g Boiling: Heat of Vaporization (  H vap ) for Water: 2256 J/g

Total Quantitative Analysis How much energy is required to convert 40.0 g of ice at –30 o C to steam at 125 o C?

Total Quantitative Analysis Convert 40.0 g of ice at –30 o C to steam at 125 o C Warm ice: (Specific heat = 2.06 J/g- o C) Melt ice: Warm water (s.h. = 4.18 J/g- o C)

Total Quantitative Analysis Convert 40.0 g of ice at –30 o C to steam at 125 o C Boil water: Warm steam (s.h. = 1.92 J/g- o C)