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Chemistry unit 1 > heat--- > Flashcards

heat--- Flashcards

1
Q

Absolute Zero

A
  • 0 K ​(-273.15 C)-

- the theoretical temperature at which gases have a velocity of 0 and are unable to move of occupy space

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2
Q

Evaporation

A
  • occurs at any temperature

- occurs only at the surface of the liquid

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3
Q

Boiling

A
  • the temperature at which vapour pressure equals the atmospheric pressure
  • occurs throughout the liquid
  • bubbles are produced
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4
Q

Why can evaporation occur below boiling point?

A
  • temperature is the average kinetic energy of particles
  • meaning that some particles have higher kinetic energy than others so some particles would have enough kinetic energy to break free at the surface of the liquid (evaporate)
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5
Q

Why Evaporation has a cooling effect?

A
  • during evaporation, the particles that break free (evaporate) at the surface of the liquid have a higher kinetic energy
  • hence when they leave the particles with lower kinetic energies are the ones left
  • since the temperature is the average kinetic energy, and the removal of higher kinetic energy particles results in a lower average kinetic energy, the temperature decreases hence having a cooling effect
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6
Q

Vapour pressure

A
  • the force of evaporated particles on unevaportaed particles per unit area
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7
Q

Factors affecting vapour pressure

A
  • temperature
  • strength of intermolecular bonds
  • impurities
  • surface area exposed
  • closed or open container
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8
Q

Evaporation vs boiling

A

Evaporation

  • occurs at any temperature
  • only occurs at the surface of the liquid
  • doesn’t produce bubbles

Boiling

  • occurs when vapour pressure equals atmospheric pressure
  • vapour forms throughout the liquid, hence bubbles
  • all particles have sufficient energy to overcome forces between them and break free
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9
Q

Why there is no temperature change in melting and boiling?

A
  • when melting and boiling is occurring all the energy is being used to move particles further away and increase the potential energy of particles
  • no energy goes towards kinetic energy and since temperature is the average kinetic energy of all particles and there is no change in kinetic energy, the temperature doesn’t change
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10
Q

Kinetic energy

A
  • the energy of vibration in the particles of a substance
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11
Q

Potential energy

A
  • energy in an object virtue of its position in relation to other particles or objects
  • the further away particles are, the greater the kinetic energy
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12
Q

Heat

A
  • amount of energy in particles
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13
Q

Temperature

A
  • the measure of the average kinetic energy of particles
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14
Q

Solubility

A
  • the physical property referring to the ability for a given substance (solute) to dissolve in another substance (solvent)
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15
Q

Explain how it is possible to use a pressure cooker containing liquid water to obtain temperatures over 100 0C. What effect does this have on the time needed for cooking?

A
  • in a pressure cooker due to the sealed area created by the lid, the atmospheric pressure acting on the liquid water is higher than in the environment outside of the pressure cooker
  • since boiling occurs when atmospheric pressure equals vapour pressure, and the atmospheric pressure is higher in the pressure cooker, so the vapour pressure needs to be higher, the temperature at which the water will boil increases
  • therefore the liquid can obtain temperatures over 100C which decreasing cooking time as the substances are exposed to higher temperatures
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16
Q

Why water boils at 108C in the darkest tunnels of Zandix, which are 3km beneath the surface of the earth?

A
  • as you go under the surface of the earth, the atmospheric pressure increases
  • since boiling occurs when vapour pressure equals atmospheric pressure, vapour pressure will have to be higher, hence boiling will occur at a higher boiling temperature
17
Q

Why water boils below 100C at Mount Everest

A
  • Mount Everest has a lower atmospheric pressure than at the ground level
  • since boiling occurs when vapour pressure equals atmospheric pressure, the vapour pressure will have to be lower, hence a lower boiling temperature
18
Q

Why steam at 100C can give a more serious burn than water at 100C

A
  • both the liquid and gas at 100C will release the same amount of heat energy as they are at the same temperature
  • however steam will also release the latent heat of vaporisation and it condenses when it comes into contact with the skin, hence causing a more severe burn
19
Q

Is the vapour pressure of water always 4.24kPa? Explain.

A
  • no, vapour pressure is teh force of evaporated particles

Chemistry unit 1 (4 decks)

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