P6 - Molecules and Matter Flashcards
(20 cards)
How do you calculate the density of an object?
Density (kg/m^3) = mass (kg) / volume (m^3)
𝜌 = m / V
How do you calculate the density of irregularly shaped objects?
Fill a displacement can with water and align a measuring beaker with the spout, make sure the water level is just below the spout. Place the object slowly into the can, not dropping it or causing a splash. Measure the volume of water displaced - this is the volume of the object.
How are particles arranged in a solid?
Particles are closely packed together. Forces between particles are strong so particles cannot move freely. They vibrate around a fixed position. Solids have a fixed shape.
How are particles arranged in a liquid?
Particles are touching and can flow over each other. They are incompressible fluids with no fixed shape that conforms to the shape of its container.
How are particles arranged in a gas?
Particles are widely spaced, they move around randomly and quickly. Particles fill the container they are in.
What is a physical change?
When a substance changes state (e.g. solid to liquid)
* They are reversible
* Mass is conserved when a substance changes state.
What is each change of state called?
Solid to liquid - melting
Liquid to gas - boiling or vaporisation
Gas to liquid - condensation
Liquid to solid - freezing
Solid to gas - sublimation
How do you cause a substance to melt or vaporise?
Supplying energy to the substance through a process of heating.
What can we observe during a change of state?
The temperature of the substance stays constant. The energy is latent (hidden) - we cannot measure a change of temperature because the energy is not transferred to the kinetic energy store of the particles.
* As a substance is cooled, the latent energy is transferred to the surroundings
What is the difference between evaporating and boiling?
Evaporation
* Only occurs at the surface
* Occurs at any temperature
* NO bubbles formed
Boiling
* Occurs within the liquid
* Only occurs at the boiling point temperature
* Bubbles appear
What is internal energy?
The energy stored by the particles of a substance.
It is the sum of:
* the mean kinetic energy of the particles due to their individual motions
* the potential energy of the particles due to their individual positions relative to each other.
How does energy in the kinetic energy stores of particles change depending on their state?
Solids have the lowest kinetic energy so only vibrate around a fixed point, liquids have more kinetic energy so the particles can slide past each other. Gases have the most kinetic energy so move around at high speed in random directions.
How does energy in the potential energy stores of particles change depending on their state?
As particles get further apart, the energy in their potential energy store increases. Solids have the least potential energy, gases have the most.
How do we increase the internal energy store of a substance?
We can increase the internal energy by heating a substance.
While the temperature of a substance is increasing energy is being transferred to the kinetic energy store of the particles.
Whereas when temperature is constant at a change of state energy is being transferred to the potential energy store of the particles.
How do you calculate specific heat capacity? when do you use it?
c = ΔE / mΔθ
This is used to find out how much energy is needed to heat 1kg of a substance 1℃ when not at the melting or boiling point.
What is the specific latent heat of fusion?
Lf - is the energy needed to change the state of 1kg of the substance from a solid to a liquid at its melting point.
Lf (J/kg) = Energy transferred (J) / mass (kg)
Lf = E / m
What is the specific latent heat of vaporisation?
Lv - is the energy needed to change the state of 1kg of the substance from a liquid to a gas at its boiling point.
Lv (J/kg) = Energy transferred (J) / mass (kg)
Lv = E / m
Why does increasing the temperature of a gas in a sealed container increase the pressure of the gas?
The energy transferred to the gas when it is heated increases the kinetic energy of its particles, so the average speed of the particles increases and they collide with each other and the walls of the container more frequently exerting a higher force, so the pressure of the gas increases as the force per unit area increases.
What happens to pressure if you reduce the volume of a fixed mass of gas at a constant temperature?
Gas pressure increases because the space the particles are moving in is smaller so they don’t travel as far between collisions with the container making more frequent collisions occur and therefore a higher pressure as more force is exerted over a smaller area.
What is Boyle’s Law?
For a fixed mass of gas at a constant temperature:
pressure, p (PA) x volume, V (m^3) = constant
P1V1 = P2V2
