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Rates of Reaction
Rates/Reactions/Catalysts and Kinetic Theory
| Question | Answer |
|---|---|
| Rate of reaction (definition) | Rate of reaction is the change in concentration of any one product or reactant per unit time |
| Factors that influence rate of reaction | 1: Nature of reactants 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 fast at room temperature (ionic). Reactions that involve the breaking and formation of bonds are generally slow at room temperature (covalent) |
| How does particle size influence rate of reaction? | The smaller particle size has a larger surface energy 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 react 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 |
| What is the relationship between Rate and Concentration? | Directly proportional |
| 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 likelihood of 2 particles colliding with each other. |
| What is a catalyst? | A catalyst is a substance that alters the rate of chemical reaction but is not 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 | Hydrogen Peroxide and Potassium Iodide |
| Give an example of heterogenous catalysis | Methanol and Platinum |
| 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 | Ethanoic Acid and Potassium Permanganate |
| 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 and 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 bonds being broken and bonds being formed. |
| What is Activation Energy? | Activation energy is the minimum energy that colliding particles must have for a successful reaction to take place. |
| What effect do catalysts have on activation energy? | Catalysts lower the activation energy of a reaction which makes it easier for the reaction to take place. |
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cbschemistry
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