Volume of Gas Produced
- in some reactions → gas is produced.
- This method only works in reactions which produce gaseous product
- can measure ROR → by observing production of gas in a given amount of time.
Key Exam Phrasing:
- Measure the volume of gas formed at regular time intervals for a fixed duration of time and plot a graph using the results. Chemistry Practical Notes
- take readings until value becomes constant
- the graph must have a changing gradient*
Sample
Q: Explain why speed of reaction decreases with time A: concentration/amt of limiting reagent is being used up refer to Concentration of Reactant(s) in Aqueous State
Change In Mass
→ as reactants get used up in reaction, mass decreases. → mass of products increases.
- Measure change in mass at regular time intervals in a fixed duration of time and plot a graph using the results
- take readings until value becomes constant
- graph must have changing gradient
- Method only works for reactions which produce gaseous products
- can determine amt of gaseous products → from the loss of mass of reaction mixture → due to the gas escaping from the reaction vessel.
- Gradient of graph is steepest at start of reaction. Hence rate of reaction is fastest at beginning
- As reaction progresses → gradient becomes gentler → rate of reaction decreases with time
- Gradient approaches 0 → mass of reaction mixture → stopped decreasing.
Note
always read axis of graph carefully → to interpret rate of reaction → than to memorise shape of graph
- shape of graph different → because y axis → shows loss in mass of reaction mixture + flask → and not mass of reaction mixture and flask.
Other
Measuring time taken for solid reactant to disappear OR time taken for a solid product to appear
- for reactions with solid reactants/products
Calculating Rate of Reaction
Formulae
Calculating Rate of Reaction
Must collect + measure quantity of the product formed using suitable apparatus
Experimental Chemistry Main Note
Common for planning questions → Chemistry Practical Notes
Important
state that you must measure time for each measurement of mass/temp/volume etc. so that you can plot a graph