Rates of Reaction

what can rate of reaction measure (2)

• how fast a product is made

• how fast a reactant is used up

what must atoms and molecules do for a reaction to be successful (2)

• collide at the correct angle

• have sufficient energy on collision to form products - the activation energy

factors affecting rate of reaction (5)

• temperature

• surface area

• concentration

• gas pressure

• catalysts

how does concentration affect rate of reaction

higher concentration means more atoms / molecules in a fixed volume. the frequency of successful collisions thus increases, increasing rate of reaction.

method for investigating how concentration affects rate of reaction using different concentrations of hydrochloric acid (6)

1. measure 50 cm³ of 2M HCl using a measuring cylinder. Pour the acid into conical flask

2. fill up trough 2/3 with water. attach a delivery tube to the conical flask, with the other end in the water trough

3. fill the other measuring cylinder with water to the brim. put hand on the top, turn it upside down, and place it in the trough on top of the open end of the delivery tube. clamp it there with the stand and clamp.

4. add a strip of magnesium to conical flask, and immediately put the bung back into the flask, and start the stopwatch

5. record volume of hydrogen gas produced every 10 seconds until the volume no longer changes

6. repeat steps 1-5 with 1M HCl and 0.5M HCl.

when are tangents used to calculate rate of reaction on graphs?

when the line is curved and the question asks for the rate of reaction at a specific point, eg at 10 secs

method for investigating how concentration affects rate of reaction using different volumes of sodium thiosulfate (6)

1. measure 25cm³ of sodium thiosulfate in a measuring cylinder. pour it into a conical flask.

2. place the conical flask on the card with the black cross on it.

3. measure 5cm³ of HCl in another measuring cylinder. pour it into the conical flask with the sodium thiosulfate in, and start the stopwatch immediately

4. look through the conical flask at the top. measure how long it takes for the cross to disappear, as the solution becomes opaque due to solid sulfur being produced

5. record the time. repeat steps 1-5 for decreasing volumes of sodium thiosulfate from 25, 20, 15, 10 and to 5cm³.

6. calculate reaction rate for each volume of sodium thiosulfate by calculating the reciprocal of the time

how does temperature affect reaction rate

atoms / molecules gain more KE at higher temperatures. they move faster, causing more frequent, successful collisions with other atoms and molecules. they collide with more energy, increasing reaction rate

method for investigating how temperature affects rate of reaction by changing temperatures of chemicals (6)

1. add sodium thiosulfate, potassium iodide and starch solution in one beaker to make chemical X. add hydrogen peroxide and sulfuric acid in another beaker to make chemical Y. label each beaker with permanent marker ‘X’ and ‘Y’

2. measure 25cm³ of chemicals X and Y into separate measuring cylinders and into separate boiling tubes. label the boiling tubes too.

3. fill a beaker with boiling / room temperature water. use a kettle or ice cubes to increase / decrease the temperature of the water. put a thermometer in the water. once it reaches the temperature required, place both boiling tubes in the beaker. put the thermometer in one of the boiling tubes

4. once the temperature stops changing, take the boiling tubes out. pour one of them into the other to start the reaction. immediately start the stopwatch.

5. measure how long it takes for the boiling tube to turn blue-black - will be instantaneous. record temperature and time. repeat steps 1-5 for different temperatures, eg 10-50 C in 10 C intervals

6. calculate reaction rate for each temperature as a reciprocal of the time taken

what are systematic, random and zero errors (3)

• systematic error - faults in equipment with consistent magnitudes of errors every experiment

• random error - measurements varying unpredictably every time. happens due to human reaction time, changes in environment

• zero error - specific type of systematic error. happens when equipment gives a false reading from a number other than zero.

What are catalysts

chemicals increasing rate of reaction but aren’t used up in the overall reaction

only very _____ amounts of catalysts are needed to increase ________ ____ between _____ amounts of __________. A catalyst is ________ to a particular reaction; different catalysts catalyse different reaction, and not all reactions have ________ catalysts. Catalysts provide an _________ _____ for the reaction that has a lower __________ ______. As a result, less _____ is required for the reaction to progress, so reactions can occur at lower ____________. Lowers energy ______ in industry, reducing _____________ costs and ______ ____ demand which contributes to global warming.

small, reaction rate, large, reactants, specific, suitable, alternate route, activation energy, energy, temperatures, demand, manufacturing, fossil fuel

method for investigating how catalysts affects rate of reaction using different catalysts (5)

1. measure 10cm³ of sodium thiosulfate into a beaker. place the beaker on the card with the cross on.

2. add 10cm³ of iron 3 nitrate, and start the stopwatch immediately.

3. measure the time taken for the cross to become visible from the top of the beaker. record the time.

4. repeat steps 1-3 but by adding the first catalyst, copper 2 sulfate, to the sodium thiosulfate before the iron 3 nitrate.

5. repeat steps 1-4 with catalysts iron 2 sulfate and then cobalt nitrate instead of copper 2 sulfate