solids liquids and gases Flashcards
Density definition
The mass per unit volume of a material
density and mass corrilation
low density materials typically have a low mass
high density materials have a high mass
gas molecules
Gases, for examples, are less dense than solids because the molecules are more spread out (same mass, over a larger volume)
units for density
g/cm3
practical: investigate density using direct measurements of mass and volume for a regular object
Independent variable = Type of shape / volume
Dependent variable = Mass of the object
- Place the object on a digital balance and note down its mass
- Use either the ruler,Vernier calipers or micrometer to measure the object’s dimensions (width, height, length, radius) – the apparatus will depend on the size of the object
- Repeat these measurements and take an average of these readings before calculating the density
- Ensure the digital balance is set to zero before taking measurements of mass
- Ensure to take repeat readings and calculate an average to keep this error to a minimum
practical: investigate density using direct measurements of mass and volume for a irregular object
- Independent variable = Different irregular shapes / mass
Dependent variable = Volume of displaced water
- Place the object on a digital balance and note down its mass
- Fill the eureka can with water up to a point just below the spout
- Place an empty measuring cylinder below its spout
- Carefully lower the object into the eureka can - water is displaced
from the eureka can via the spout into a measuring cylinder;
the volume of water displaced is equivalent to the volume of
the object - Measure the volume of the displaced water in the measuring cylinder
- Repeat these measurements and take an average before calculating the density
- determine the volume of water displaced into the
measuring cylinder by observing the scale at the bottom of
the meniscus, at eye level to avoid parallax error: - Place the irregular object in the displacement can carefully, as dropping it from a height might cause water to splash which will lead to an incorrect volume reading
pressure definition
The concentration of a force or the force per unit area
force and area correlation
Pressure is the action of a force over an area; if a force is spread over a large area it
will result in a smaller pressure whereas if the force acts over only a small area it will
result in a larger pressure
untis for pressure
N/cm2
pascals
,
understand how the pressure at a point in a gas or liquid at rest acts equally in all directions
When an object is immersed in a fluid, the fluid will exert pressure, squeezing the object
The pressure exerted on objects in fluids creates forces against surfaces
These forces act at 90 degrees (at right angles) to the surface
The amount of pressure exerted increases with depth:
The force from the pressure is exerted evenly across the whole surface of an object in a liquid, and in all directions
solid
The molecules are very close together and arranged in a regular pattern
The molecules vibrate about fixed positions
A definite shape (they are rigid)
A definite volume
liquid
- The molecules are still close together (no gaps) but are no longer arranged in a regular pattern
The molecules are able to slide past each other
No definite shape – they are able to flow and will take the shape of a container
A definite volume
gasses
- The molecules are widely separated - about 10 times further apart in each direction
The molecules move about randomly at high speeds
Gases are highly compressible, this is because:
There are large gaps between the particles
It is easier to push the particles closer together than in solids or liquids
what happens from soild to liquid
When a solid melts to form a liquid the strong bonds between the particles holding
them in fixed positions are broken - new weaker bonds now form between the
particles, but these allow the particles to move freely over one another
liquid evaporates or boils to form a gas
When a liquid evaporates or boils to form a gas the bonds between the particles
holding them close together in the liquid state are broken - enabling the particles to
break free and so move freely from one another
effect of temp
Heating - increasing the kinetic energy of its particles
This increase in kinetic energy (and therefore energy stored in the system) can:
- Cause the temperature of the system to increase
- produce a change of state (solid to liquid or liquid to gas)
The higher the temperature, t - the higher the average kinetic energy of the molecules and vice versa
This means they move around faster
practical: obtain a temperature - time graph to show the constant temperature during a change of state
Fill an insulated beaker with crushed ice straight from the freezer
- Place the ice cubes in the beaker (it should be about half full)
- Place the thermometer in the beaker
- Place the beaker on the tripod and gauze and slowly start to heat it using the bunsen burner
- As the beaker is heated, take regular temperature measurements (e.g. at one minute intervals)
Continue this whilst the substance changes state (from solid to liquid)
- Ensure the thermometer is held vertically in the beaker
- Ensure there are enough ice cubes to surround the
thermometer in the beaker, and only begin the experiment when the temperature is below 0 - with crushed ice straight from the freezer
specific heat capacitty definition
The specific heat capacity of a substance is the amount of thermal energy (in Joules)
required to raise the temperature of 1 kg of that substance by 1 °C
Different substances have different specific heat capacities
If a substance has a low specific heat capacity, it heats up and cools down quickly (ie. it takes less energy to change its temperature)
If a substance has a high specific heat capacity, it heats up and cools down slowly (ie. it takes more energy to change its temperature)
5.11P practical: obtain a temperature - time graph to show the constant temperature
during a change of state
Fill an insulated beaker with crushed ice straight from the freezer
o Insert a heater, thermometer and stirrer into the crushed ice
o Switch on the stirrer and heater and start a stopwatch - record the initial
temperature of the ice
o At frequent intervals e.g. every 15 seconds record the temperature and
continue until the ice has completely melted into water
o Plot a graph of temperature against time
how to make the practical investigate the specific heat capacity of materials including water and some solids experiment for fare
The value obtained will be higher than the official value (4,200 J/kg °C) because some
thermal energy will be transferred to the surroundings by conduction, convection or
radiation - this can be reduced by increased use of insulation around the container
* To increase reliability - repeat the experiment, check for anomalous results, discard
them if present and then calculate a mean value for the specific heat capacity
ABSOLUTE 0 temp
- Eventually it reaches a point where the particles stop vibrating; it no longer has any thermal energy and cannot be cooled any more - this temperature is -273 °C and is called absolute zero
5.14P practical: investigate the specific heat capacity of materials including water and some solids
Use an electronic balance to measure the mass of an empty polystyrene container
then add water and measure the mass again; the difference in mass is the mass of the
water in the container
* Add a heater, stirrer and thermometer to
the water and then cover with a lid to
reduce heat loss
* Record the initial temperature
* Connect the heater to a power supply,
start a timer and simultaneously switch on
the current to the heater and stirrer
Record the reading on the ammeter and the supply voltage
* Heat the water until its temperature has risen approximately 15 °C then
simultaneously switch off the current to the heater and stirrer, record the maximum
temperature of the water, stop the timer and record the time that the water has
been heated
what are the molecules in gas like
Molecules in a gas are in constant random motion at high speeds
Molecules in a gas are in constant random motion and so collide frequently with the walls of the container - their collisions exert a force on the surface area of the
to converts from decress c to k (kelvins)
- from C to K –> +273
from k to C –> minus 273
whay does an increase of temp do to gas molecuels
- As you increase the temperature of a gas, the kinetic energy of the gas particles
increases and therefore their average speed also increases
