Topic 3: Particle Model of Matter Flashcards
What is internal energy?
The total energy stored inside a system by the particles that make up the system due to their motion and positions
What two stores do molecules within a substance have energy in?
- Kinetic
- Potential
How does heating change substance’s internal energy?
Increasing kinetic energy and store of particles
What does an increase in kinetic and internal energy do to a system?
- Temp. of system to increase
- Change of state
What happens to energy transfer when a substance reaches a certain temperature during heating?
Energy stops being transferred to the kinetic store of the molecules and is instead transferred to their potential store.
What does the energy transferred to the potential store do during a change of state?
It overcomes the intermolecular forces of attraction, causing the molecules to move further apart.
What happens to the potential energy of molecules during a change of state?
The potential energy increases, allowing the molecules to overcome intermolecular forces.
What happens to the kinetic energy and temperature during a change of state?
The kinetic energy remains the same, so the temperature stays constant even though heating continues.
Give an example of a change of state caused by energy transfer to the potential store.
A liquid changing to a gas (e.g., water boiling into steam).
What is the increase in temperature of a system dependent on?
- The mass of the substance heated
- The type of material
- The energy input to the system
What is the definition for the specific heat capacity of a substance?
The amount of energy required to raise the temperature of 1 kg of the substance by 1 °C
What is the equation for specific heat capacity?
ΔE = mcΔθ
Where:
ΔE = change in energy, in joules (J)
m = mass, in kilograms (kg)
c = specific heat capacity, in joules per kilogram per degree Celsius (J/kg °C)
Δθ = change in temperature, in degrees Celsius (°C)
What does it mean for a substance to have a low specific heat capacity?
- Heats up and cools quickly
- Takes less energy to change its temperature
What does it mean for a substance to have high specific heat capacity?
- Heats up and cools slowly
- Takes more energy to change its temperature
What is specific heat capacity mainly used for?
Liquids and Solids
What does the specific heat capacity of different substances determine?
How useful they would be for a specific purpose e.g best material for kitchen appliance
What is the specific heat capacity of aluminium?
910 J/kg°C
What is the specific heat capacity of copper?
390 J/kg°C
What is the specific heat capacity of lead?
126 J/kg°C
What is the specific heat capacity of glass?
500-680 J/kg°C
What is the specific heat capacity of water?
4200 J/kg°C
What is the specific heat capacity of mercury?
140 J/kg°C
What is density?
Mass per unit volume of a material
What is the equation for density?
p = m/V
Where:
p = Density (kgm⁻³)
m = Mass (kg)
V = Volume (m³)
What are the units for density?
g/cm³ or kg/m³
What is the particle model and what does it explain?
- Describes arrangement and movement of particles in a substance
- Explains:
> Different states of matter
> Physical properties (differences in density)
Describe a solid in terms of particle model
- Particles are closely packed
- Vibrate at fixed positions
- Definite shape and volume
Describe a liquid in terms of particle model
- Particles are closely packed
- Flow over one another
- No definite shape but definite volume
Describe a gas in terms of particle model
- Particles are far apart
- Move randomly
- No definite shape or fixed volume
- Highly compressible due to large gaps
What are the differences in density of solid and liquid?
- Molecules are tightly packed in both
- Density roughly the same
What is the density of a gas?
- Molecules separated
- Significantly low density
- Density is 1/1000 of solid or liquid
What is the common density for water and air at sea level?
Water - 1000 kg/m³
Air at Sea Level - 1.3 kg/m³
What happens to the number of molecules and mass during change of state?
- No. of molecules doesn’t change
- Mass doesn’t change
Are changes of state reversible?
Yes, physical not chemical change
What is latent heat?
The energy needed for a substance to change state without changing temperature
What happens to temperature during a change of state?
Temperature remains constant despite energy being transferred
Why does temperature remain constant during state changes?
Energy is used to overcome intermolecular forces rather than increasing kinetic energy
What are the two types of latent heat?
Latent heat of fusion and latent heat of vaporization
What is latent heat of fusion?
The energy required to change a substance from solid to liquid state
What is latent heat of vaporization?
The energy required to change a substance from liquid to gas state
What happens to molecules during melting?
They gain enough energy to overcome forces holding them in rigid solid structure
What happens to molecules during boiling?
They gain enough energy to move completely apart from one another
Why do molecules in a solid need energy to become liquid?
To overcome the tight intermolecular bonds in the solid structure
Why do molecules in a liquid need energy to become gas?
To overcome the intermolecular forces keeping them close together
What changes during a phase transition?
Internal energy changes but temperature remains constant
What happens on a heating curve during melting or boiling?
The graph shows a flat line (plateau) where temperature remains constant
What are the two types of of latent heat?
- Latent heat of fusion
- Latent heat of vaporisation
What is specific latent heat?
The amount of energy required to change the state of 1 kg of a substance with no change in temperature
What is the difference between specific latent heat of fusion and vaporisation?
Fusion is changing state between a solid and liquid whilst vaporisation is changing state between liquid and gas
What is the definition for specific latent heat of fusion?
The energy required to convert 1 kg of a substance between a solid and a liquid state with no change in temperature
What is the symbol and unit for latent heat?
- L
- J/kg
What is the definition for the specific latent heat of vaporisation?
The energy required to convert 1 kg between a liquid and a gaseous state with no change in temperature
What is the equation for specific latent heat?
E=mL
Where:
E- Thermal Energy required for a change of state (in joules)
m- Mass (in kilograms)
L- Specific Latent heat (in J/kg)
What are the specific latent heat values for water?
Fusion- 330kJ/kg
Vaporisation- 2.26 MJ/kg
What do heating and cooling graphs summarize?
Heating and cooling graphs summarize: 1) How temperature changes when energy is transferred to or away from a substance, and 2) Where changes of state occur.
What happens during heating of a substance?
Energy is transferred TO the substance and the kinetic energy of molecules increases.
What happens during cooling of a substance?
Energy is transferred AWAY from the substance and the kinetic energy of molecules decreases.
What happens at the melting point during heating?
The temperature stops increasing as energy is used to overcome intermolecular forces, causing the substance to change from solid to liquid.
What happens at the boiling point during heating?
The temperature stops increasing as energy is used to overcome intermolecular forces, causing the substance to change from liquid to gas.
What is the process of a gas turning back into a liquid called?
Condensation
What is the process of a liquid turning back into a solid called?
Freezing
What stays constant during a change of state?
Temperature remains constant during changes of state (melting, freezing, vaporization, condensation).
What type of energy increases during the flat portions of the heating curve?
Potential energy increases as intermolecular forces are overcome.
What type of energy increases during the sloped portions of the heating curve?
Kinetic energy increases as particles move faster.
Why does temperature remain constant during a change of state?
Because the energy transferred is being used to overcome intermolecular forces (changing potential energy) rather than increasing particle motion (kinetic energy).
What determines the steepness of the sloped sections on a heating/cooling curve?
The specific heat capacity of the substance in that state (solid, liquid, or gas).
What is the process of a liquid turning back into a solid called?
Freezing
What does the first upward-sloping line on a heating curve represent?
The solid phase, where temperature increases as energy is added and kinetic energy of particles increases.
What does the first flat/horizontal line on a heating curve represent?
The solid-to-liquid transition (melting), where temperature remains constant as energy is used to overcome intermolecular forces.
What does the second upward-sloping line on a heating curve represent?
The liquid phase, where temperature increases as energy is added and kinetic energy of particles increases.
What does the second flat/horizontal line on a heating curve represent?
The liquid-to-gas transition (vaporization/boiling), where temperature remains constant as energy is used to overcome intermolecular forces.
What does the third upward-sloping line on a heating curve represent?
The gas phase, where temperature increases as energy is added and kinetic energy of particles increases.
Describe what happens during the melting portion of a heating curve.
Temperature remains constant as energy is used to overcome intermolecular forces in the solid, converting it to a liquid.
Describe what happens during the vaporization portion of a heating curve.
Temperature remains constant as energy is used to overcome intermolecular forces in the liquid, converting it to a gas.
Describe what happens during the condensation portion of a cooling curve.
Temperature remains constant as energy is released, allowing intermolecular forces to pull gas molecules together to form a liquid.
Describe what happens during the freezing portion of a cooling curve.
Temperature remains constant as energy is released, allowing intermolecular forces to arrange liquid molecules into a solid structure.
What happens to pressure during compression?
Volume decreases, pressure increases
What happens to pressure during expansion?
Volume increases, pressure decreases
Why is there a greater net force on walls during an increase in pressure?
- Pressure produces a net force at right angles to the wall of the gas container (or any surface)
- When gas is compresses, molecules hit walls more frequently therefore having greater net force
True or False: Pressure and Volume are directly proportional to each other
False, they are indirectly proportional to each other
What is Boyle’s Law?
Initial Pressure x Volume = Final Pressure x Volume
What happens when work is done on a gas?
Energy is transferred to the gas; Internal energy increases; Temperature typically increases
What happens during gas compression?
A force pushes a piston, decreasing the volume; Gas molecules move faster (higher kinetic energy); Temperature increases
What happens when a gas expands?
The gas does work on its surroundings; The gas loses energy; Temperature decreases
How does a bicycle pump demonstrate work done on a gas?
When a thumb covers the end and the pump is compressed; Work is done on the trapped air; The pump becomes noticeably warmer; This demonstrates conversion of mechanical work to thermal energy
How do diesel engines use gas compression?
A mixture of gas and fuel is rapidly compressed; Compression causes the gas to heat up significantly; The heat ignites the fuel (no spark plug needed)
What happens when pressurized CO₂ is released from a cylinder?
The gas does work as it expands; The gas loses energy; Temperature drops dramatically; Can cause CO₂ to freeze into dry ice (solid CO₂)
How does the direction of work affect gas temperature?
Work done ON the gas (compression) → Temperature rises; Work done BY the gas (expansion) → Temperature falls
