Rate and extent of chemical reactions
The rate of reaction is how quickly the reactants turn into products. It can be measured in
many ways: volume of gas produced per second (cm^3/s) or mass lost or gained per
second (g/s). These ways calculate the mean rate of reaction; the equation is generally
change in quantity over time.
The practical's you can do to conclude rate of reaction are:
- Disappearing cross experiment; where you place a conical flask over a piece of
paper with a black cross drawn on it. Measure a fixed volume of sodium thiosulfate
and pour it into the conical flask. Measure a fixed volume of one concentration of
hydrochloric acid and pour into the same conical flask. Immediately the time for the
cross to disappear due to the solution getting cloudy as sulfate forms a white
precipitate. Repeat with different concentrations of hydrochloric acid (if measuring
effect of concentration) or repeat using different temperatures (if measuring effect
of temperature).
- Volume of gas; connect a conical flask to a gas syringe using a bung and delivery
tube. Add substances that make a gas and measure the volume of gas produced
per second with the syringe. Repeat with different concentrations of one substance
or different temperatures.
- Change in mass: add two substances to a conical flask that react e.g. acid and
metal. Put conical flask on balance, record initial and final mass, and work out
mass change (either increase or decrease). Decrease usually means a gas was
produced and escaped.
Collision theory is the idea that particles need to collide with enough energy to react. If
they don't collide with enough energy, the reaction will not be successful. This is followed
by activation energy, which is the minimum energy required for particles to react; a lower
activation energy results in a greater rate of reaction.
The rate of reaction can be plotted on a graph with the change in quantity over time. The
reaction will either decrease or increase but eventually flatline as either the products or
reactants get used up.
- From the graph you can measure the rate of reaction from one time by drawing a
tangent at that time and working out the gradient.
The conditions that impact the rate of reactions are temperature, pressure, concentration,
surface area, and catalyst.
The rate of reaction is how quickly the reactants turn into products. It can be measured in
many ways: volume of gas produced per second (cm^3/s) or mass lost or gained per
second (g/s). These ways calculate the mean rate of reaction; the equation is generally
change in quantity over time.
The practical's you can do to conclude rate of reaction are:
- Disappearing cross experiment; where you place a conical flask over a piece of
paper with a black cross drawn on it. Measure a fixed volume of sodium thiosulfate
and pour it into the conical flask. Measure a fixed volume of one concentration of
hydrochloric acid and pour into the same conical flask. Immediately the time for the
cross to disappear due to the solution getting cloudy as sulfate forms a white
precipitate. Repeat with different concentrations of hydrochloric acid (if measuring
effect of concentration) or repeat using different temperatures (if measuring effect
of temperature).
- Volume of gas; connect a conical flask to a gas syringe using a bung and delivery
tube. Add substances that make a gas and measure the volume of gas produced
per second with the syringe. Repeat with different concentrations of one substance
or different temperatures.
- Change in mass: add two substances to a conical flask that react e.g. acid and
metal. Put conical flask on balance, record initial and final mass, and work out
mass change (either increase or decrease). Decrease usually means a gas was
produced and escaped.
Collision theory is the idea that particles need to collide with enough energy to react. If
they don't collide with enough energy, the reaction will not be successful. This is followed
by activation energy, which is the minimum energy required for particles to react; a lower
activation energy results in a greater rate of reaction.
The rate of reaction can be plotted on a graph with the change in quantity over time. The
reaction will either decrease or increase but eventually flatline as either the products or
reactants get used up.
- From the graph you can measure the rate of reaction from one time by drawing a
tangent at that time and working out the gradient.
The conditions that impact the rate of reactions are temperature, pressure, concentration,
surface area, and catalyst.
