physic chapter 9 Flashcards
When a material is heated at constant pressure
- Its temperature increases
- Its overall volume increases (it expands)
- Its density decreases
why does expansion happen
- The molecules start to move around (or vibrate) faster as they gain kinetic energy
- This causes them to collide with each other more often and push each other apart
explain why solids expand slightly
The low energy molecules cannot overcome the intermolecular forces of attraction holding them together
by how much does the solid expand
Expands slightly
why do solids, liquids and gases expand by different amounts
This behaviour is influenced by the distances and strength of the forces between particles in each state
by how much does the liquid expand
Expands more than solids
explain why liquids expand more than solids
The molecules have enough energy to partially overcome the intermolecular forces of attraction holding them together
by how much does the gas expand
Expand significantly
why does the gas expand significantly
The high energy molecules have enough energy to completely overcome the intermolecular forces of attraction holding them together
what are the applications of thermal expansion
- Liquid-in-glass thermometers
- Temperature-activated switches
what are the consequences of thermal expansion
The expansion of solid materials can cause them to buckle if they get too hot
these may include, railway lines, bridges and shrink fitting
what is the internal energy
the internal energy of a substance is the total energy of all its particles
what affects the temperature of a substance
- the mass of the substance
- type of material
- amount of energy transferred to a thermal store
define specific heat capacity
the amount of thermal energy required to raise the temperature of a unit mass of substance by 1 degrees celsius
how can we calculate the specific heat capacity
thermal energy required / temperature change x mass of a substance
what are some of the commonly used units to measure the specific heat capacity
joule per kilogram per degree celsius ( J/Kg * C)
how is specific heat capacity determined
- Place the beaker on the digital balance and press ‘zero’
- Add approximately 250 ml of water and record the mass of the water using the digital balance
- Place the immersion heater and thermometer in the water
- Connect up the circuit as shown in the diagram, with the ammeter in series with the power supply and immersion heater, and the voltmeter in parallel with the immersion heater
- Record the initial temperature of the water at time 0 s
- Turn on the power supply, set it at approximately 10 V, and start the stopwatch
- Record the voltage from the voltmeter and the current from the ammeter
- Continue to record the temperature, voltage and current every 60 seconds for 10 minutes
- Repeat steps 2-8, replacing the beaker of water for the solid block of aluminium and starting with recording its mass using the digital balance
how can we calculate the specific heat capacity of the aluminium
change in thermal energy = average current x average potential difference x time spent heating
the melting and boiling points are also known as
the fixed point
at which temperature does the pure water boil
100 degrees celsius
describe what happens during melting
The particles in a solid are held in fixed positions by strong bonds. Energy is needed to bre bonds. When the bonds are broken, the particles can move out of their fixed positions and slightly further apart from each other. The solid has melted. Melting takes place at the melting point without a change in temperature.
at which temperature does the ice melt
0 degrees celsius
describe what happens during boiling
The particles in a liquid have strong forces between them. Energy is needed to break the bonds and separate the particles further apart. Energy is also required for the particles to overcome the atmospheric pressure in order to escape into the air. When these happen, the liquid has boiled.
Boiling takes place at the boiling point without a change in temperature.
describe what happens during condensation
The reverse of boiling occurs. When a gas condenses into a liquid, forces pull the particles closer and energy is released.
describe what happens during solidification
The reverse of melting occurs. Strong forces pull the particles in a liquid into fixed positions to form a solid. energy is released.
what is evaporation
Evaporation is a change in state of a liquid to a gas
when can evaporation happen
- At any temperature
- Only from the surface of a liquid
explain the occurrence of evaporation using the kinetic theory of matter
- The molecules in a liquid are always moving randomly at different speeds
- At the surface, the liquid molecules that have enough energy to overcome the downward attractive forces of the other liquid molecules and the atmospheric pressure escape into the atmosphere.
- The less energetic molecules are left behind. The average kinetic energy of the molecules in the liquid decreases, and therefore the average temperature of the liquid decreases.
the rate of evaporation is affected by:
temperature, surface area of the liquid, movement of air
why does evaporation cause cooling
he average energy of the liquid is reduced when the particles with most energy leave. Therefore liquids are cooled down by evaporation
what is the difference between evaporation and boiling
boiling
- occurs at a particular temperature
- relatively fast
- takes place throughout the liquid
- bubbles are formed in the liquid
- temperature remains constant
evaporation
- Occurs at any temperature
- Relatively slow
- Takes place only at the liquid surface
- No bubbles are formed in the liquid
- Temperature may change
what causes the rise of internal energy
the rise in temperature
describe the liquid in glass thermometer
A liquid-in-glass thermometer relies on the expansion of liquids to measure temperature
It consists of a thin glass capillary tube containing a liquid that expands with temperature
describe the temperature activated switches
Temperature-activated switches utilise a bimetallic (made from two types of metal) strip
It consists of two metals that expand at different rates and bends by a predictable amount at a given temperature
Internal energy is defined as:
the internal energy of a substance is the total energy of all its particles
what does the motion affect
Motion of the particles affects their kinetic energy
what does the positions affect
Positions of the particles relative to each other affects their potential energy
describe the average kinetic energy
Heating a system changes a substance’s internal energy by increasing the kinetic energy of its particles
The temperature of the material, therefore, is related to the average kinetic energy of the molecules
what increases the average kinetic energy
An increase in temperature leads to an increase of the average kinetic energy of the particles in the substance
This also means that internal energy increases, as internal energy is the sum of all kinetic and potential energies
what is the aim of the experiment of investigating the specific heat capacity
The aim of the experiment is to determine the specific heat capacity of a substance, by linking the decrease of one energy store (or work done) to the increase in temperature and subsequent increase in thermal energy stored
