P1 Flashcards
What (and when) did Dalton propose about atoms?
everything was made of indivisible tiny spheres called atoms in 1800
What key discovery did JJ Thomson make in 18XX?
1897 - He discovered the electron and proposed the Plum Pudding Model.
What did the Plum Pudding Model suggest?
Atoms are a sphere of positive charge with negative electrons dispersed within it. - cancel out charges
What experiment did Rutherford conduct in 1911?
The Gold Foil Experiment (carried out by Geiger and Marsden).
What did Rutherford’s experiment reveal about atomic structure?
most alpha particles went straight through - atom mainly empty space
some slightly deflected - nucleus must be +, hence repelling other + charges
Few particles deflected >90 - nucleus has most mass in atom
What was the Bohr model in 1913?
Electrons exist in orbitals (shells) - doesn’t get attracted to + nucleus otherwise atom would collapse
What subatomic particles are found in the nucleus of an atom?
Protons and neutrons.
What are the relative mass and charge of a proton?
Mass = 1, Charge = +1.
What are the relative mass and charge of a neutron?
Mass = 1, Charge = 0.
What are the relative mass and charge of an electron?
Mass ≈ 0.0005 Charge = -1.
Where are electrons found in an atom?
In energy levels (orbitals/shells) at different distances from the nucleus.
How big is a typical atom?
About 1 × 10⁻¹⁰ metres.
Where is most of an atom’s mass concentrated?
In the nucleus.
What is the definition of density?
Mass per unit volume.
What is the formula for density?
ρ = m / V (density = mass / volume)
What are the units of density?
kg/m³ or kgm^-3
What does density depend on?
The spacing of the atoms in matter.
Why do solids and liquids generally have higher densities than gases?
Because the space between particles in solids and liquids is small. - more particles in the same volume than gas
Why do gases have lower densities?
Gas particles are far apart and have high energy, occupying a larger volume. - less particles in a given volume
What is an exception where a solid is less dense than a liquid?
Ice is less dense than water.
What happens to mass during a change of state?
It is conserved (remains the same).
Do changes of state affect the density of a substance?
Yes, because the volume changes.
Are changes of state physical or chemical?
Physical – they are reversible and retain the material’s properties.
What is the difference between heat and temperature?
Temperature = average kinetic energy of particles (measured on a relative scale);
Heat = energy (measured on an absolute scale).
What are the two outcomes when a substance gains heat energy?
- It raises in temperature but stays in the same state.
- It changes state but stays at the same temperature.
What is specific heat capacity (c)?
The energy needed to raise the temperature of 1 kg of a substance by 1ºC (or 1K)
What is the formula for heat energy with specific heat capacity?
E = m × c × ∆T
What are the units for specific heat capacity?
J/kg°C
What is specific latent heat (l)?
The energy needed to change the state of 1 kg of a substance without temperature change.
What is the formula for energy with latent heat?
E = m × l
What are the units for specific latent heat?
J/kg or Jkg^-1
What is specific latent heat of fusion (or melting)?
energy transferred when 1kg of substance changes from solid to liquid state or visa versa
What is specific latent heat of vaporisation?
energy transferred when 1kg of substance changes from liquid to gas state
How do particles move in a fluid?
They move randomly in all directions.
What are fluids?
Liquids or gases.
What is the formula for pressure?
Pressure = Force / Area
(p = F / A)
Pressure measures in pascals Pa
In which direction does pressure produce a net force?
At right angles to any surface.
What happens to pressure when temperature increases (at constant volume)?
Pressure increases.
Why does increasing temperature increase pressure in a fluid?
Particles gain kinetic energy, move faster, and collide more frequently and forcefully with container walls. - closed system only
What is the proportional relationship between pressure and temperature (at constant volume)?
Pressure ∝ Temperature (p ∝ T)
What happens to a gas when pressure changes?
gas is compressed or expanded
How are volume and pressure related (at constant temperature)?
They are inversely proportional. (p ∝ 1/V)
What happens to pressure if volume increases?
Pressure decreases, because collisions occur less frequently per unit area.
What happens to pressure if volume decreases?
Pressure increases, because particles collide more often with each other and the container in a smaller space.
How are temperature and volume related (at constant pressure)?
They are directly proportional. (V ∝ T)
What happens to volume as temperature increases (at constant pressure)?
Volume increases to maintain constant pressure.
What happens to a fluid’s temperature when work is done on it?
The temperature increases. - such as a bicycle pump
What is the formula for work done involving pressure and volume?
Work done = Pressure × Volume
(W = p × V)
How can pressure increase by adding more gas?
More particles cause more collisions, transferring energy and raising temperature.
How can reducing volume heat a fluid?
Particles collide more frequently, increasing pressure and kinetic energy, thus increasing temperature.
What assumption is made about Earth’s atmospheric temperature?
It is assumed to be isothermal (same temperature throughout).
How does the atmosphere interact with solar and terrestrial radiation?
It is transparent to solar radiation but opaque to terrestrial radiation.
What assumption is made about atmospheric density?
It is assumed to be uniform density.
What is atmospheric pressure?
The total weight of the air above a unit area at a given altitude.
What happens to atmospheric pressure as altitude increases?
It decreases, because there are fewer air molecules above
Why does a helium balloon expand as it rises?
Lower external pressure means the helium inside exerts more force, causing expansion.
When does the expansion of a balloon stop?
When internal and external pressures reach equilibrium (usually it bursts before this).
When does an object float in a fluid?
When its weight is less than the weight of fluid it displaces.
What happens if an object’s weight is more than the displaced fluid?
It sinks.
What must happen for a 1000kg boat to float?
It must displace 1000kg of water before fully submerging.
What causes pressure in a liquid to vary?
Depth and density of the liquid.
What is the upward force on an object in a liquid called?
Upthrust (Buoyancy force) – it counteracts the object’s weight.
Why does a ping pong ball float?
Its density is less than water, so it displaces enough water to balance its weight.
Why does pressure increase with water depth?
The weight of the water column above increases.
What is the formula for pressure due to a liquid column?
p = h × ρ × g
(pressure = height × density × gravitational field strength)
What is the value of g (gravitational field strength) used in calculations?
10 N/kg
Why is upthrust created?
Pressure increases with depth
So pressure at bottom of object is greater than pressure at the top
The difference in pressure creates a net upward force - upthrust
For an object to float, what does the upthrust need to be equal to?
Needs go be equal to weight of object
Upthrust equation
Upthrust = force from bottom - force from top
= (pressure x area at bottom) - (pressure x area at top)
= weight of object (if floating in equilibrium)
