Measuring Rates of Reaction

Vocabulary flashcards covering methods for measuring the rate of chemical reactions, including mass loss, gas collection, and precipitation techniques.

Rate of reaction

A measurement of how fast a reactant is used up or how fast a product is made during a chemical reaction.

Rate of reaction equation

$\text{Rate} = \frac{\text{amount of reactant used}}{\text{time taken}}$ or $\text{Rate} = \frac{\text{amount of product made}}{\text{time taken}}$

Units for rate (Mass)

When mass is measured in grams, the units for rate are $g/s$.

Units for rate (Volume)

When volume is measured in $cm^3$ or $dm^3$, the units for rate are $cm^3/s$ or $dm^3/s$.

Mass loss method

A method used to determine the rate of reaction by measuring the decrease in mass as a gas escapes from the reaction vessel over time.

Cotton wool

Material placed in the neck of a conical flask during mass loss experiments to allow gas to escape while preventing materials from being ejected or splashed out.

Mass loss limitation for Hydrogen

The method is unsuitable for hydrogen because its relative formula mass ($M_r = 2$) is too small to be accurately measured on a $2$ or $3$ decimal place balance.

Gas collection method

A technique used to find the rate of reaction by trapping a gaseous product and measuring its volume over time.

Downward displacement of water

A gas collection setup where gas enters an inverted measuring cylinder and displaces the water inside.

Gas syringe

An alternative apparatus for gas collection that measures the volume of gas produced over time without using water.

Precipitation method

A method used to measure the rate of reaction by tracking the formation of a solid precipitate which clouds the reaction mixture.

Disappearing cross experiment

An experiment where the time taken for a precipitate to block a cross drawn on paper from view is measured.

Subjective error

A disadvantage of the disappearing cross method where different people may not agree on the exact moment the cross disappears.

Relative formula mass ($M_r$) for Carbon dioxide

A value of $44$ which makes it sufficiently dense to be measured using the mass loss method.

Precipitation reaction example

$$\text{Sodium thiosulfate} + \text{hydrochloric acid} \rightarrow \text{sodium chloride} + \text{sulfur dioxide} + \text{water} + \text{sulfur}$$