SHC,+PHASE+CHANGES+AND+LATENT+HEAT

IB PHYSICS > THERMAL PHYSICS
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SHC, PHASE CHANGES, LATENT HEAT
Define //specific heat capacity// and //thermal capacity//.

THERMAL CAPACITY: The amount of thermal energy required to raise the temperature of an object by 1K. SPECIFIC HEAT CAPACITY: The amount of thermal energy required to raise the temperature of 1kg of a substance by 1K.
 * ~ Substance ||~ SHC/Jkg -1 K -1 ||
 * Aluminium || 900 ||
 * Alcohol || 2400 ||
 * Copper || 390 ||
 * Glass || 840 ||
 * Iron/ steel || 450 ||
 * Lead || 130 ||
 * Marble || 860 ||
 * Mercury || 140 ||
 * Silver || 230 ||
 * Wood || 1700 ||
 * Ice || 2100 ||
 * Water || 4186 ||
 * Steam || 2010 ||
 * Human body (ave) || 3470 ||
 * Protein || 1700 ||

WHY ARE SHCs DIFFERENT? Temperature is a measure of average random kinetic energy. Internal energy is the sum of PE and KE (in IB assuming particles are points and do not vibrate or rotate).



To change the temperature of a substance requires an increase in internal energy.



= = Solve problems involving specific heat capacities and thermal capacities.

Explain the physical differences between the solid, liquid and gaseous phases in terms of molecular structure and particle motion. Only a simple model is required. [|MP AND BP IN THE PERIODIC TABLE SIMULATION] [|STATES OF MATTER SIM ON PHET] MICROSCOPIC DESCRIPTION: Considers properties of matter at a particle level. Molecules are in motion and collide with each other and the container. KINETIC ENERGY OF PARTICLES: Temperature is a measure of the average kinetic energy of the particles. PHASES OF MATTER: Particles in a solid are locked into the crystal structure and do not have enough KE to escape. In a liquid, they overcome the chemical bonds but cannot separate completely for the other atoms. The particles in a gas have enough KE to escape from each other.



Describe and explain the process of phase changes in terms of molecular behaviour. Students should be familiar with the terms melting, freezing, evaporating, boiling and condensing, and should be able to describe each in terms of the changes in molecular potential and random kinetic energies of molecules.



Explain in terms of molecular behaviour why temperature does not change during a phase change.



Distinguish between evaporation and boiling.

EVAPORATION: The process by which faster-moving molecules escape from the surface of a liquid. This results in a cooling of the liquid. BOILING: The process by which a liquid changes into a solid at the constant temperature of the boiling point. Define //specific latent heat//.

SPECIFIC LATENT HEAT: The amount of thermal energy required to change the state of 1kg of a substance without a change in temperature. SLH of fusion is solid to liquid; SLH of vaporisation is liquid to gas.

 Solve problems involving specific latent heats. In solving SHC and SLH questions, it is important to begin with a word equation How much heat is required to change 50g of ice at -10°C to steam at 100°C? Total Q = Q to warm ice + Q to melt ice at 0°C + Q to warm water + Q to boil water at 100°C
 * ~ Substance ||~ MP/°C ||~ SLH fusion/ kJ/kg ||~ BP/°C ||~ SLH vaporisation kJ/kg ||
 * Oxygen || -218.8 || 14 || -183 || 210 ||
 * Nitrogen || -210.0 || 26 || -195.8 || 200 ||
 * Ethyl alcohol || -114 || 104 || 78 || 850 ||
 * Ammonia || -77.8 || 33 || -33.4 || 137 ||
 * Water || 0 || 333 || 100 || 2260 ||
 * Lead || 327 || 25 || 1750 || 870 ||
 * Silver || 961 || 88 || 2193 || 2300 ||
 * Iron || 1808 || 289 || 3023 || 6340 ||
 * Tungsten || 3410 || 184 || 5900 || 4800 ||
 * EXAMPLE **

Problems may include specific heat calculations.