gas calculations and stoichiometry Flashcards
energy efficiency characteristics
energy transformations are not 100% efficient, whereby energy is generally lost as thermal energy
define percentage efficiency
a measure of how much energy supplied is transformed into final form of useful energy.
formula for percentage efficiency
experimental/theoretical x 100= output/input
define accuracy
how close a measurement is to its true value
define precision
how close a measurement is to each other
are accuracy and precision independent or dependent
they are independent, a result may be inaccurate but have high precision
define errors
the difference between the measured value and the true value
define systematic errors
readings differ from the true value in a consistent manner due to the equipment within the experiment
- effects the accuracy
define random errors
affects measurements in unpredictable ways
- usually occurs due to environment or instrumentation
-affects precision
- temperature fluctuations are not random due to them being confounding variable
how can we minimise heat loss
- add lid
- foil funnel heat into beaker to act is insulator
-bring flame closer to water - insulate sides of beaker
heat loss errors
- heat loss is consistent in direction and size hence is a systematic error
- amount of heat loss in random amounts each time, hence is random error
- accuracy is improved by reducing heat loss
- electric thermometer improves instrumentation used which reduces random errors and improving precison
sample response for improving accuracy
to improve the accuracy of the set up, change made. this reduces the amount of how it minimises heat loss. this decreases the effect of systematic error, which increases the accuracy of the experiment
define stoichiometry
use of coefficients in the chemical equation to indicate the proportion of 2 substances in a reaction.
unknown/known
factors that affect how much volume a gas will occupy
- temperature
-pressure - amount (moles)
formula for volume occupied by gases
n=v/vm
=vm=24.8 L/mol
mass volume stoichiometry
used when mass of a substance is given, and you have to find the volume of another substances
volume - volume stoichiometry
when volume of one substance is given and you have to find the volume of another substance
when can volume of reactants and products be multiplied by coefficients?
-pressure is constant
- temperature is constant
- all in gaseous state
-cant be done for mass
how to find limiting and excess reagents
- find mol of both reagents
- divide by coefficients or multiply by unknown/known
- compare amounts - limiting reagent has less than found
