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Define specific heat capacity
- The energy required to change the temperature (of a substance) by 1℃/1K;
- of mass 1kg / per unit mass.
7 Assumptions of an ideal gas
- Point molecules / negligible volume;
- No forces between molecule except for in contact;
- Motion / distribution is random;
- Elastic collisions / no energy lost;
- Obey Newton's laws of motion;
- Collision in zero time;
- Gravity is ignored;
The molecular weight of the substance in grams / 6.02x10^25 atoms of the substance / same number of particles as in 12g of Carbon-12;
Define internal energy
Total energy of component particles / comprises of potential energy + (random) kinetic energy. Measured in Joules (J);
- Measure of average kinetic energy of particles;
- indicates direction of (natural) flow of thermal energy;
- measured in Kelvin (K);
Describe cooling by evaporation
- Faster / more energetic molecules escape during evaporation;
- slower/ less energetic lower temperature molecules remain;
- so internal energy removed from body;
Describe the difference in internal energy of a solid and an ideal gas.
- Internal energy of solid is total KE plus PE of molecules;
- the molecules of an ideal gas comprises of KE only;
Explain why the latent heat of vaporization is larger than the latent heat of fusion.
- In boiling, energy is required to break bonds (in vaporization) and to separate molecules;
- in melting (more) energy is available to overcome bond energies of molecules without large separation;
Distinguish between evaporation and boiling.
- Evaporation at surface of liquid, boiling occurs throughout liquid;
- evaporation occurs at all temperatures, boiling at boiling point only;
Define thermal capacity
Thermal energy required to change temperature by 1K / 1℃;
Define thermal equilibrium
Rate of energy absorption is equal to the rate of energy emission / temperature of substance remains constant;
The (non-mechanical) transfer of energy;