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16 Rates of Reaction
Rates/Reactions/Catalysts and Kinetic Theory
| Question | Answer |
|---|---|
| Rate of reaction (definition) | is the change in concentration of any one product or reactant per unit time |
| Factors that influence rate of reaction | 1: Nature of reactants (Ionic/Covalent) 2: Particle size 3: Concentration 4: Temperature 5: Presence of a catayst |
| Why are ionic reactions faster than covalent? | Reactions that involve the coming together of oppositely charged particles are generally instantaneous(ionic). Reactions that involve the breaking and formation of bonds are generally slow (covalent) |
| How does particle size influence rate of reaction? | The smaller particle size has a larger surface area and therefore a faster rate of reaction |
| What 3 things are needed for a dust explosion to occur? | Small particle size, oxygen and a spark (source of ignition) |
| How does concentration influence rate of reaction | Generally speaking the higher the concentration of the reactants the faster the rate of reaction as there is more particles of the chemicals to collide with each other. |
| How do the graphs for concentration vs rate of reaction differ? | The graph for the higher concentration has a steeper curve which indicates a faster rate. Both graphs will have the same end point as they produce the same amount of product. |
| What substance is liberated when Hydrochloric Acid is reacted with Sodium Thiosulphate? | Sulphur |
| What is the relationship between Time and Concentration? | Inversely proportional, the more concentrated the less time needed for the reaction |
| What is the relationship between Rate and Concentration? | Directly proportional, as the concentration increases the rate increases |
| What is the relationship between temperature and rate of reaction | Generally speaking the rate of reaction increases as temperature rises as the particles with more heat energy move at a faster rate and this increases the number of effective collisions. |
| What is a catalyst? | A catalyst is a substance that alters the rate of chemical reaction without being used up in the reaction itself |
| What catalyst is found in livers? | Catalase |
| What do we call a catalyst that slows down a chemical reaction? | Negative catalyst or inhibitor |
| Properties of a catalyst (4) | 1: Catalysts remain unchanged after a catalyst. 2: Catalysts are specific and will only speed up one reaction. 3: Only a small amount of catalyst is required. 4: Catalysts can be destroyed by catalytic poisons, eg lead |
| 3 types of catalysis? | Homogenous catalysis, Heterogenous catalysis, Autocatalysis |
| Example of homogenous catalysis | reactants & catalysts in the same phase eg Hydrogen Peroxide and Potassium Iodide |
| Give an example of heterogenous catalysis | reactants & catalysts are in different phases eg Methanol (liquid) and Platinum (solid) |
| 2 products produced and 2 observations when Platinum catalyses the decomposition of methanol | Hydrogen and ethanal are produced. The Platinum glows red and the Hydrogen produced burns with a pop |
| Give an example of autocatalysis | when one of the products of the reaction acts as a catalyst for the reaction eg Potassium Permanganate & Ethanedioic acid. Mn2+ ions act as a catalyst. |
| 2 theorys to explain how catalysts work | 1: The Surface Adsorption Theory 2: The Intermediate Compound Theory |
| Which scientist put forward the Intermediate Compound Theory? | Arrhenius. It states that the catalyst forms an intermediate compound with one of the reactants and this compound reacts with the second reactant to form the products and regenerate the catalyst. |
| Example of a reaction that demonstrates the intermediate compound theory | 1: Hydrogen Peroxide and Potassium Iodide (Iodine Snake) 2: The reaction of Potassium Sodium Tartate and Hydrogen Peroxide can be catalysed by Cobalt Chloride |
| What colour change is seen when Potassium Sodium Tartate and Hydrogen Peroxide is catalysed by Cobalt Chloride | The reaction starts out as Pink. Turns green as the intermediate compound is formed. Then back to pink as the intermediate compound is used up. |
| What is the difference between ABsorption and ADsorption? | ABsorption occurs when a material penetrates the surface of another material. Adsorption occurs when one material is taken onto the surface of another material. |
| What reaction demonstrates the surface adsorption theory? | The catalysis of Hydrogen and Oxygen by Platinum. |
| What does desorption mean? | Desorption is the removal of a chemical from the surface of a material. |
| Dangerous reactions that occur in a cars engine? | 1: Nitrogen reacts with Oxygen to Nitrogen Oxide. 2: Nitrogen Oxide then reacts with Oxygen to form Nitrogen Dioxide 3: Carbon Monoxide is formed by the incomplete combustion of fuel |
| Catalysts found in a cars catalytic converter? | Platinum, Palladium and Rhodium. |
| What do the catalysts in a catalytic converter change the harmful gases produced by a car engine into? | Carbon Monoxide to Carbon Dioxide Nitrogen Monoxide and Nitrogen Dioxide to Nitrogen Unused hydrocarbons to Carbon Dioxide and Water |
| What is an effective collision? | An effective collision is one which results in the formation of products. |
| What is Activation Energy? | Activation energy is the minimum energy that colliding particles must have for a reaction to occur |
| What effect do catalysts have on rates of reactions? | Catalysts make it easier for the reaction to take place by providing an alternative pathway with a lower activation energy. |
| The instantaneous rate | is the rate of reaction at any one particular time during the reaction. |
| an enzyme | is a biological catalyst |
Created by:
Ms O'Farrell
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