Particle Model Flashcards
What is density?
Density (p) = mass / volume
G/cm3 or kg/m3
What is a solid?
- strong forces of attraction hold particles together in a fixed and regular arranged position
- particles have little energy inKE stores so only vibrate in fixed position
What is a liquid?
- forces or attraction between particles are weaker
- particles are close together but can flow in irregular arrangements at low speeds
- they have more KE in stores
What is a gas?
- there are almost no forces of attraction between the particles
- more energy in their KE stores than liquids
- free to move in random directions at high speeds
Where is thermal energy stored?
The energy in a substance’s thermal energy store is held together by its particles in their kinetic energy stored
-when you heat something the extra energy is transferred into the KE stores making them move faster or vibrate more wearing the forces
What happens when there is a change in state?
Mass is conserved (particles are the same)
-these physical changes differ from some chemical changes because the material recovers its original properties if the change is reversed
What happens to the density when there is a change in state?
- it’s volume changes as particles gets further apart of closer together
- therefore seeing as D = m/v its density must too
- substances are verbally more dense as solids and least dense as gases
What is the equation for specific heat capacity?
Change in thermal energy = mass(Kg) x specific heat capacity (J/Kg°C) x temperature change (°C)
DeltaQ = m x c x delta temp
What is specific heat capacity?
Is the change in energy in the substance’s thermal energy stores needed to raise the temperature of 1KG of that substance by 1°C
What does heating do?
Increases energy in thermal energy stored or internal energy of the substance (sum of energy in KE stores and of the particles)
-temperature is in theory a way of measuring average internal energy of a substance
What is the specific heat capacity of water?
4200 J/KG°C
What is specific latent heat?
The amount of energy needed to change 1KG of it from one state to another without changing its temperature
What is specific latent heat in terms of cooling and heating?
-for cooling SLH is the energy released by a change in state
What is the name for SLH for different states?
For changing between a solid and a liquid it is called the specific latent heat of fusion
-for changing between a liquid and a gas it is the specific latent heat if vaporisation
What is the equation for specific latent heat?
Thermal energy (J) = mass (Kg) x specific latent heat (J/Kg) Q = m x L
What is 0 Kelvin equal to?
-273°C
What is the latent heat of fusion and vaporisation for water?
Melting ice = 0°
Vaporisation = 100°
On a graph which sections show latent heat?
The flat parts
What is pressure?
- colliding has particles create pressure
- when gas particles more randomly they collide and exert a force and so pressure
- in a sealed container the outward gas pressure is the total force exerted by all of the particles in the gas on a unit area of the container walls
How does gas pressure vary with volume?
Increasing the volume of a gas means the particles and hit the walls of the contained less often
- this means gas pressure decreases, they are inversely proptional
- decreasing volume means they are in a smaller space so more collisions with container walls so pressure increases
What is the equation that links gas pressure and volume?
- for a gas of fixed mass at a constant temperature: p1v1 = p2v2
- p1 is the pressure at a volume 1 and p2 is the pressure at a volume v2
- pressure is measured in Pa or N/m2
What effect does temperature have on gas pressure?
The higher the temperature the faster the particles move and the more often they collide with the container.
- the force exerted by each particle during a collision also increases as the temperature increases
- increasing temperature of a fixed volume increases its pressure
What is absolute Zero?
In theory the coldest that anything can get is -273°C
- here the particles have as little energy in their kinetic stores as it’s possible to get (almost still)
- this is the start of the Kelvin scale of temperature (a temp change of 1° is a cha be of 1 Kelvin
How do you convert between kelvins and degrees?
Degrees Celsius to kelvins, just add 273
-Kelvin to degrees Celsius just subtract 273
What does the pressure of a gas produce?
- the collisions between particles happen in random directions but add together to produce a net overall force at right angles to the wall of the container
- the outside of a gas container will also be under pressure from whatever’s around it (unless it’s a vacuum)
For objects without a fixed volume, when is there volume constant?
When the internal pressure of the gases inside pushing out is equal to the pressure of the air outside pushing inwards
- so you can change this volume by changing the internal or external pressures
- e.g. a balloon
How can you expand or compress gases?
Through a pressure change
Why can doing work on a gas increase it’s temperature with the example of a gas pump?
- in a bike pump the gas exerts a pressure on the plunger of the pump and so exerts a force, work had to be done against this force to push down the plunger
- this transferred energy to the kinetic energy stores of the gas particles so increases its internal energy and hence temperature
- if the pump is connected to something, some might also be transferred to to the objects thermal energy store
How do you change the pressure of a gas inside the container?
By heating or cooling
- as heated gas particles gain more energy and more quicker, increasing pressure due to more collisions
- the outward pressure of object is now larger than inward pressure from surroundings so the balloon expands until the pressures are equal again
- cooling has the inverse effect, so the gas inside the balloon is compressed
How can you change the external pressure on a balloon?
- for a gas in an air tight syringe, pushing hard on the plunger increases the inward pressure on the gas so they it is larger than the outward pressure so gas internally is compressed
- atmospheric pressure decreases with altitude increase so inward pressure decreases so the gas expands
What is the equation for pressure?
- the force per unit area
- P=F/A
What is fluid pressure?
Fluid pressure is the pressure caused by the collisions of gas and liquid particles on a given surface and the surrounding atmospheric pressure
-as the area of this surface increases the pressure exerted decreases
What is fluid pressure dependent on?
- assuming particles have the same mass , a denser fluid has more particles in a given space so more are able to collide and so pressure is higher
- as depth of a fluid the number of particles above that point increases so the weight of these particles adds to the pressure felt here so fluid pressure increases with depth
How do you calculate the magnitude of the pressure in liquids and differences with depth?
Pressure due to column of a liquid (Pa) = height of column (m) x density of liquid (kg/m3) x gravitational field strength N/kg)
P = hpg
What is atmospheric pressure?
Is created on a surface by air molecules colliding with the surface and exerting a Force
How does atmospheric pressure vary with altitude?
-as altitude increases atmospheric pressure decreases
(Graph is curved as it also affected by density that varies with height)
-as altitude increases, atmosphere gets less dense so there are fewer air molecules that are able to collide with the surface
-this also means the weight of the air above it decreases
What is upthrust?
A resultant Force
-it is equal to the weight of the fluid that has been displaced by the object
Why is an object submerged in an object subject to upthrust?
- when an object is submerged in a fluid, the pressure of the fluid exerts a force on it in every direction
- pressure increases with depth so the force exerted on the bottom of the object is larger than the force acting on the top of the object causing a resultant Force
How does an object float?
- if the upthrust of an object is equal to the object’s weight then the forces balance and the object floats as it can displaced enough water
- it it is more than the upthrust it sinks at is is unable to displace enough fluid to equal its weight so it’s weight is larger than upthrust
What happens if the object is less dense that the fluid it is placed in?
It displaces a volume of fluid that is equal to its weight before it is completely submerged
- at this point the objects weight is equal to the upthrust so the object floats
- as it rises the amount of water displaced decreases and therefore it rises until the weight of water displaced is equal to that of its weight
What does pressure in a fluid cause?
A force normal (right angles) to any surface
