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TOPIC 3
THERMAL PHYSICS
THERMAL CONCEPTS
SOLID LIQUID GAS
particles closely packed together particles slightly more spread out particles very spread out strong forces between particles ⇒ vibrate about fixed positions weaker forces between particles ⇒ can move past each other negligible forces between particles ⇒ more randomly fixed shape takes shape of the container no fixed shape fixed volume fixed volume no fixed volume cannot be compressed cannot be compressed can be easily compressed ⇒ molecules are held together by intermolecular forces
TEMPERATURE AND ABSOLUTE TEMPERATURE
HEAT: transfer of internal energy between objects ⇒ from higher to lower energy
*objects in thermal equilibrium have the same temperature
TEMPERATURE: describe how hot or cold an object is and determines the direction of
heat flow between two bodies ⇒ measure of the average random KE of particles ● the vibration and movement of particles depend on the temperature ● as temperature increases, KEavg increases ● the SI unit for temperature is the kelvin (K) ● ABSOLUTE ZERO is 0 on the Kelvin scale (-273°C) ⇒ the temperature at which all movement of particles stops temperature (K) = temperature (°C) + 273. GOOD THERMOMETER: linear expansion (expands equally) + long range of temperature
INTERNAL ENERGY: sum of total KE (thermal energy) + total PE
⇒ KE is associated with random / translational rotational motions of molecules directly related to temperature higher T°C ⇒ higher KE ⇒ PE is associated with stretching and compression of the intermolecular bonds as particles move amount depends on: forces between particles + how far apart they are further ⇒ weaker ⇒ more PE
SPECIFIC HEAT CAPACITY: the amount of energy required to
raise the temperature of 1g / 1kg of a substance by 1°C ⇒ applies to a substance - eg: water and oil ‘c’ ⇒ measure of how easily a material can absorb or release internal thermal energy
HEAT CAPACITY: the amount of energy required to raise the
temperature of an object by 1°C ⇒ applies to an object - eg: calorimeter, beaker, spoon
LATENT HEAT: the amount of energy required to break/make bonds
between molecules at a phase change w/no temperature change ***** phase: solid, liquid, gas LATENT HEAT OF FUSION: solid to liquid LATENT HEAT OF BOILING/VAPORIZATION: liquid to gas A) solid - particles vibrate w/larger amplitude ⇒ Q = mcΔT B) solid to liquid - melting ⇒ Q = mL (fusion) C) liquid - molecules gain KE so move around faster ⇒ Q = mcΔT D) liquid to gas - boiling ⇒ Q = mL (boiling/vaporization) E) gas - molecules gain KE so move around faster ⇒ Q = mcΔT BOILING: only occurs at the boiling point (specific temperature depending on substance) and occurs throughout the liquid EVAPORATION: can occur at any temperature and only occurs at the surface of the liquid
PHASE CHANGE
CHANGE OF PHASE PROCESS KE PE
SOLID ⇒ LIQUID melting unchanged ⬆ LIQUID ⇒ GAS boiling unchanged ⬆ GAS ⇒ LIQUID condensation unchanged ⬇ LIQUID ⇒ SOLID freezing unchanged ⬇ During a phase change, temperature and KE remain constant and PE changes ⇒ PE⬆: molecules spread out ⇒ PE⬇: molecules get closer together
REAL GAS
● forces exist between gas molecules ⇒intermolecular forces ● the volume of molecules is not negligible compared to the volume of gas ⇒ may behave similarly to ideal gases under high temperature and low pressure
OTHER LAWS
MOLE / MOLAR MASS & AVOGADRO’S CONSTANT
AVOGADRO’S CONSTANT: 6.02 x 10^23 mol-
MOLE: fixed number of particles and refers to the amount of substance (n)
⇒ the n° of particles in a mole of a substance = Avogadro’s Constant
MOLAR MASS: mass of 1 mole of a substance (g mol-1)
⇒ numerically equal to its relative atomic mas
