topic 7 - rates of reaction and energy changes Flashcards
(48 cards)
rate of reaction formula
time
what are three ways of measuring reaction rate
change in mass
volume of gas given off
precipitation
describe how rate of reaction is measured in terms of change in mass (when a gas is produced)
using a mass balance
as the gas is released, the lost mass is easily measured on the balance (the quicker the reading is dropping, the higher the reaction rate)
plot graph of change in mass against time elapsed
what should you do if the gas being released is dangerous
use a fume cupboard
describe how rate of reaction is measured in terms of volume of gas given off
using a gas syringe
the more gas given off in set time interval, the faster the reaction
once no more gas is produced, the reaction is finished
plot results on graph of gas volume against time elapsed
describe how rate of reaction is measured in terms of a precipitation
two reactant solutions are mixed in a flask which is placed on a piece of paper with a mark on it
observe the mark through the mixture and time how long it takes for it to be obscured (the faster the mark disappears, the faster the reaction)
why is measuring rate of reaction in terms of a precipitation subjective
people may have different opinions on when the mark disappears
what three factors affect reaction rate
surface area
concentration/pressure
temperature
the steeper the slope on a rate of reaction graph…
the faster the rate of reaction
to find the gradient on a curve
draw a tangent and calculate the gradient of that straight line
that gradient is the rate at that point
investigating the effect of surface area on rate of reaction: uses what reactants
hydrochloric acid
marble chips
investigating the effect of surface area on rate of reaction: describe the method
measure volume of gas with a gas syringe (taking readings at regular intervals and recording them in a table)
plot results on a graph (volume against time)
repeat with the same VOLUME and CONCENTRATION of acid and same MASS of chips but with the chips MORE crushed up, to increase surface area
REPEAT
investigating the effect of surface area on rate of reaction: results
the finer the particles, the greater the rate of reaction
investigating the effect of concentration on rate of reaction: uses what reactants
hydrochloric acid
marble chips
investigating the effect of concentration on rate of reaction: describe the method (2 possible)
OR
–
measure the change in mass during the reaction
place a flask with a set concentration of HCl on a mass balance
add marble chips and immediately note the mass shown on the balance
record the mass at regular intervals
plot mass lost against time on a graph
repeat with different concentrations of acid
investigating the effect of temperature on rate of reaction: reactants and reaction
observed colour change from precipitation reaction between sodium thiosulfate and hydrochloric acid
investigating the effect of temperature on rate of reaction: describe the method (6/7)
1) (sodium thiosulfate solution and hydrochloric acid react to form a yellow precipitate of sulfur)
2) measure out fixed volumes of the two solutions using a measuring cylinder
3) gently heat both solutions to the desired temperature using a water bath before mixing them
4) mix solutions in a conical flask and place flask over a black mark
5) time how long it take for the mark to disappear as the precipitate forms
6) repeat at different temperatures
7) plot results on graph of time taken for mark to disappear against temperature of reacting solutions
investigating the effect of temperature on rate of reaction: results
increasing temperature, increases rate of reaction
activation energy
the minimum energy that particles need in order to react when they collide
AND
the minimum amount of energy for bonds to break
why does increasing temperature, increase rate of reaction
when temperature increases, particle have more kinetic energy so move more quickly
when they move more quickly, there are more frequent collisions
therefore at higher temperatures, THERE WILL BE MORE SUCCESSFUL COLLISIONS, increasing rate of reaction
why does increasing concentration/pressure, increase rate of reaction
if a solution is more concentrated, there are more reactant particles in the same volume/are more crowded so collisions are more likely and the rate of reaction increases
why does increasing surface area, increase rate of reaction
increasing the surface area of an object gives it a greater surface area to volume ratio
the particles surrounding it have a larger area to work on so the frequency of collisions will increase
this increases rate of reaction
catalyst
a substance that increases the rate of reaction without being chemically change or being used up in the reaction itself
how do catalysts increase rate of reaction
catalysts lower the activation energy needed for a reaction to occur by providing an ALTERNATIIVE REACTION PATHWAY (which has a lower activation energy)
therefore, more particles have the minimum amount of energy needed for a reaction when particles collide so more successful collisions occur
