(b) Rates of reaction

3:09 describe experiments to investigate the effects of changes in surface area of a solid, concentration of a solution, temperature and the use of a catalyst on the rate of a reaction

The rate of a chemical reaction can be measured either by how quickly reactants are used up or how quickly the products are formed.

The rate of reaction can be calculated using the following equation:

The units for rate of reaction will usually be grams per min (g/min)

 

An investigation of the reaction between marble chips and hydrochloric acid:

Marble chips, calcium carbonate (CaCO3) react with hydrochloric acid (HCl) to produce carbon dioxide gas. Calcium chloride solution is also formed.

Using the apparatus shown the change in mass of carbon dioxide can be measure with time.

As the marble chips react with the acid, carbon dioxide is given off.

The purpose of the cotton wool is to allow carbon dioxide to escape, but to stop any acid from spraying out.

The mass of carbon dioxide lost is measured at intervals, and a graph is plotted:

 

Experiment to investigate the effects of changes in surface area of solid on the rate of a reaction:

The experiment is repeated using the exact same quantities of everything but using larger chips. The reaction with the larger chips happens faster.

Both sets of results are plotted on the same graph.

 

Experiment to investigate the effects of changes in concentration of solutions on the rate of a reaction:

The experiment is again repeated using the exact same quantities of everything but this time with half the concentration of acid. The marble chips must however be in excess. The reaction with the half the concentration of acid happens slower and produces half the amount of carbon dioxide.

 

Experiment to investigate the effects of changes in temperature on the rate of a reaction:

The experiment is once again repeated using the exact same quantities of everything but this time at a higher temperature. The reaction with the higher temperature happens faster.

 

Experiment to investigate the effects of the use of a catalyst on the rate of a reaction:

Hydrogen peroxide naturally decomposes slowly producing water and oxygen gas.

Manganese (IV) oxide can be used as a catalyst to speed up the rate of reaction.

The rate of reaction can be measured by measuring the volume of oxygen produced at regular intervals using a gas syringe.

Both sets of results are plotted on the same graph.

 

 

 

 

 

 

 

Experiment to investigate the reaction between varying concentrations of sodium thiosulfate and hydrochloric acid

Sodium thiosulfate (Na2S2O3) and hydrochloric acid (HCl) are both colourless solutions. They react to form a yellow precipitate of sulfur.

To investigate the effects of changes in concentration of sodium thiosulfate on the rate of a reaction, the conical flask is placed above a cross. The reaction mixture is observed from directly above and the time for a cross to disappear is measured. The cross disappears because a precipitate of sulfur is formed.

In order to change the concentration of sodium thiosulfate, the volumes of sodium thiosulfate and water are varied (see results table). However the total volume of solution must always be kept the same as to ensure that the depth of the solution remains constant.

In this reaction, sulfur dioxide gas (SO2), which is poisonous is produced therefore the experiment must be carried out in a well ventilated room.

The results are recorded in the table below and then plotted onto a graph.

Volume of Na2S2O3(aq) (cm3)Volume of water (cm3)Concentration of Na2S2O3(aq) (mol/dm3)Time taken for cross to disappear (s)Rate of reaction (s-1) (1/time)
5000.10450.0222
40100.08600.0167
30200.06800.0125
20300.04130.0769
10400.022550.0039

The graph shows that the rate of reaction is directly proportional to the concentration.

The experiment can also be repeated to show how temperature affects the rate of reaction.

In this experiment the concentration of sodium thiosulfate is kept constant but heated to range of different temperatures.

As a rough approximation, the rate of reaction doubles for every 10oC temperature rise.

 

2018-04-25T21:48:11+00:00Categories: (b) Rates of reaction, 3 Physical chemistry, Spec2017|Tags: , |

3:10 describe the effects of changes in surface area of a solid, concentration of a solution, pressure of a gas, temperature and the use of a catalyst on the rate of a reaction

Increasing the surface area of a solid increases the rate of a reaction.

Increasing the concentration of a solution increases the rate of a reaction.

Increasing the pressure of a gas increases the rate of a reaction.

Increasing the temperature increases the rate of a reaction.

Using a catalyst increases the rate of a reaction.

3:11 explain the effects of changes in surface area of a solid, concentration of a solution, pressure of a gas and temperature on the rate of a reaction in terms of particle collision theory

Increasing the surface area of a solid:

  • more particles exposed
  • more frequent collisions
  • increase the rate of a reaction

 

Increasing the concentration of a solution or pressure of a gas:

  • more particles in same space
  • more frequent collisions
  • increase rate of reaction

 

Increasing the temperature:

  • particles have more kinetic energy
  • more frequent collisions
  • and a higher proportion of those collisions are successful because the collision energy is greater or equal to the activation energy
  • increase rate of reaction

 

2018-04-25T21:48:11+00:00Categories: (b) Rates of reaction, 3 Physical chemistry, Spec2017|Tags: , |

3:15 practical: investigate the effect of changing the surface area of marble chips and of changing the concentration of hydrochloric acid on the rate of reaction between marble chips and dilute hydrochloric acid

The rate of a chemical reaction can be measured either by how quickly reactants are used up or how quickly the products are formed.

The rate of reaction can be calculated using the following equation:

The units for rate of reaction will usually be grams per min (g/min)

 

An investigation of the reaction between marble chips and hydrochloric acid:

Marble chips, calcium carbonate (CaCO3) react with hydrochloric acid (HCl) to produce carbon dioxide gas. Calcium chloride solution is also formed.

Using the apparatus shown the change in mass of carbon dioxide can be measure with time.

As the marble chips react with the acid, carbon dioxide is given off.

The purpose of the cotton wool is to allow carbon dioxide to escape, but to stop any acid from spraying out.

The mass of carbon dioxide lost is measured at intervals, and a graph is plotted:

 

Experiment to investigate the effects of changes in surface area of solid on the rate of a reaction:

The experiment is repeated using the exact same quantities of everything but using larger chips. The reaction with the larger chips happens faster.

Both sets of results are plotted on the same graph.

 

Experiment to investigate the effects of changes in concentration of solutions on the rate of a reaction:

The experiment is again repeated using the exact same quantities of everything but this time with half the concentration of acid. The marble chips must however be in excess. The reaction with the half the concentration of acid happens slower and produces half the amount of carbon dioxide.

 

2018-04-25T21:48:12+00:00Categories: (b) Rates of reaction, 3 Physical chemistry, Spec2017|Tags: , |
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Section 1: Principles of chemistry

      a) States of matter

      b) Atoms

      c) Atomic structure

     d) Relative formula masses and molar volumes of gases

     e) Chemical formulae and chemical equations

     f) Ionic compounds

     g) Covalent substances

     h) Metallic crystals

     i) Electrolysis

 Section 2: Chemistry of the elements

     a) The Periodic Table

     b) Group 1 elements: lithium, sodium and potassium

     c) Group 7 elements: chlorine, bromine and iodine

     d) Oxygen and oxides

     e) Hydrogen and water

     f) Reactivity series

     g) Tests for ions and gases

Section 3: Organic chemistry

     a) Introduction

     b) Alkanes

     c) Alkenes

     d) Ethanol

Section 4: Physical chemistry

     a) Acids, alkalis and salts

     b) Energetics

     c) Rates of reaction

     d) Equilibria

Section 5: Chemistry in industry

     a) Extraction and uses of metals

     b) Crude oil

     c) Synthetic polymers

     d) The industrial manufacture of chemicals