Practical 1 - The Linear Expansion of Various Liquids Flashcards
Thermal expansion coefficient, plotting data, improvements to practical.
Give the equation for finding the volumetric thermal expansion coefficient (alpha v=subscript) for a constant pressure system, p, where: T is temperature (in Kelvin); V is volume; and Vi (subscript) is the initial volume.
alpha v = change in volume / (change in temperature x initial volume)
(this is an approximation - only a model)
In general, what do substances do when their temperature changes?
Expand/contract (in all directions).
What does it mean if alpha v is larger for a given material?
The more it will expand per unit temperature increase.
Why do ethanol (and acetone) expand more than water?
Water is more attracted to itself due to polar attractions/hydrogen bonds between molecules.
Ethanol and acetone have non-polar bonds.
Using the equation:
change in volume/change in temperature = initial volume x thermal expansion coefficient
What is the dependent variable?
Change in volume.
Using the equation:
change in volume/change in temperature = initial volume x thermal expansion coefficient
What is the independent variable?
Change in temperature.
(x-axis and left of a table)
Using the equation:
change in volume = initial volume x thermal expansion coefficient x change in temperature
What shape is the trendline expected to be?
Straight and through the origin.
What does the volumetric thermal expansion coefficient tell us?
The change in volume of any given liquid for a temperature change.
Why do liquids only have a volumetric thermal expansion coefficient?
They do not have a shape of their own so only undergo volume expansion.
Why do liquids have higher volumetric thermal expansion coefficients than solids?
The intermolecular forces present in liquids are relatively weak and its constituent molecules are more mobile. Therefore, when you heat liquids they expand much more in volume.
How should you plot a graph for this experiment?
- title
- labelled axes with units
- in pencil
- lines of best fit through the origin and
labelled with the name of the liquid
Instead of drawing the graph negative, positive values could’ve been plotted. What should you do before making this decision in the future?
Check if it works for the individual experiment (in this case it would).
The value of acetone was quite different, why was this the case?
- Due to the resolution of the serological
pipette. - The rapid temperature change when
cooling.
The value of the volumetric thermal expansion coefficient for water was often too high for a lot of groups, how could this be changed if repeating the experiment?
Boil water first to prevent out-gassing.
(Out-gassing = release of gas due to temperature change).
Why is the y-intercept 0 for:
change in volume = initial volume x alpha v x change in temperature
The initial volume and alpha v are constants and y = mx + c for a linear function, so c=0.
