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Kinetics

Kinetics. Click to start. The rate increases with time because the acid becomes more dilute. The rate decreases with time because the acid becomes more dilute. A. B. The rate decreases with time because the magnesium carbonate particls get smaller.

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Kinetics

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  1. Kinetics Click to start

  2. The rate increases with time because the acid becomes more dilute. The rate decreases with time because the acid becomes more dilute. A B The rate decreases with time because the magnesium carbonate particls get smaller. The rate increases with time because the magnesium carbonate particls get smaller. C D Question 1 The reaction between excess magnesium carbonate and hydrochloric acid can be followed by measuring the volume of carbon dioxide produced with time. The results of one such reaction are shown below. How does the rate of this reaction change with time and what is the main reason for this change? Volume of CO2 Time 0

  3. Wrong Answer! The magnesium carbonate is present in excess, hence there is little change in surface area. Try Again

  4. A B total reaction time total mass of hydrogen formed average rate of production of hydrogen gas C initial reaction rate D Question 2 Zinc reacts with sulfuric acid as shown below. Zn(s) + H2SO4(aq)  ZnSO4(aq) + H2(g) Two identical samples of zinc powder were reacted with separate samples of excess acid as follows: Reaction 1 : zinc added to 0.5 moldm-3 sulfuric acid Reaction 2 : zinc added to 2.0 moldm-3 sulfuric acid What is the same for reaction 1 and 2? ?

  5. Wrong Answer! Zinc is the limiting reagent and hence determines the volume of the hydroge gas. The 2 samples of zinc have the same mass. Try Again

  6. Provides a new mechanism or pathway with lower activation energy needed in a reaction. A Changes the sign of the enthalpy, ΔH, for the reaction. B Decreases the activation energy Ea ,for the forward reaction only. C Increases the enthalpy change ΔH, for the reaction. D Question 3 Which of the following is true for a catalyst ?

  7. Wrong Answer! Catalysts lower the activation energy for the forward and backward reactions. They provide a new mechanism or pathway. Try Again

  8. The concentration of nitrogen is too high, which slows the reaction. The molar mass of nitrogen molecules is less than that of chlorine molecules. A B Nitrogen and chlorine molecules are both non-polar molecules. Very few nitrogen and chlorine molecules have sufficient kinetic energy to react. C D Question 4 The reaction between nitrogen and chlorine in the atmosphere under normal conditions is extremely slow. Which statement best explains this?

  9. Wrong Answer! Very few colliding molecules have kinetic energies equal to or in excess of the activation energy. Try Again

  10. A collision frequency activation energy increases increases B activation energy activation energy increases does not change C activation energy activation energy does not change decreases activation energy collision frequency increases increases D Question 5 The rate of a reaction between two gases increases when the temperature is increased and a catalyst is added. Which statements are correct for the effect of these changes on the reaction? Increasing the temperature Adding a catalyst

  11. Wrong Answer! Activation energy does not vary with temperature. Try Again

  12. A mol dm-3 s-1 B mol (dm-3)2 s-1 C mol dm-3 mol s-1 D Question 6 What are the usual units for rate?

  13. Wrong Answer! Rate is defined as change in concentration (mol dm-3 ) with time (s) Try Again

  14. A 1.0 moldm-3 HCl and CaCO3 chips B 2.0 moldm-3 HCl and CaCO3 chips C 2.0 moldm-3 HCl and CaCO3 powder 4.0 moldm-3 HCl and CaCO3 powder D Question 7 For the reaction: 2HCl(aq) + CaCO3(s)  CaCl2(aq) + H2O(l) + CO2(g) Which gives the fastest rate?

  15. Wrong Answer! This combination has acid of the highest concentration and the greatest surface area for the calcium carbonate. Both these factors maximise the collision rate. Try Again

  16. A I only B II only C III only None of the above D Question 8 Excess magnesium was added to a beaker of aqueous hydrochloric acid on a balance. A graph of the mass of the beaker and contents was plotted against time (line 1). • What change in the experiment could • give line 2? • The same mass of magnesium • but in smaller pieces. • II. The same volume of a more • concentrated solution of • hydrochloric acid • III. A lower temperature Mass Line 1 Line 2 Time

  17. Wrong Answer! The addition of hydrochloric acid of higher concentration means that the reaction will go faster and hence the loss in mass will be faster. In addition, since the acid is the limiting reagent then a greater total volume of gas is lost and a greater mass loss results. Try Again

  18. A This change increases the density of the reactant particles. B This change increases the concentration of the reactant. C This change exposes more reactant particles to a possible collision. This change alters the electrical conductivity of the reactant particles. D Question 9 Which statement explains why the speed of some chemical reactions increased when the surface area of the reactants is increased?

  19. Wrong Answer! The reaction takes place on the surface. The collision rate will be directly proportional to the rate. Try Again

  20. A Rusting of iron B Sodium placed in water Reaction between hydrogen and oxygen Reaction between reactive metals with acid C D Question 10 Which of the following reactions do not occur rapidly?

  21. Wrong Answer! The reaction between reactive metals (including sodium) with water and acid is generally very fast. Rusting is a slow process. Try Again

  22. A The bonds become weaker. B The activation energy decreases. The number of molecules with the necessary kinetic energy increases. C The number of molecular collisions increases. D Question 11 The rate of many reactions increase rapidly with small increase in temperature. Which of the following best accounts for this behaviour?

  23. Wrong Answer! An increase in temperature does increase the collision rate, but the rise in proportion of molecules colliding with kinetic energies equal to or in excess of the activation increases is the major underlying reason for the rapid increase in rate. Try Again

  24. A O2 B Br C O BrO D Question 12 In the reaction shown below, which species may be acting as a catalyst? O3 + Br  BrO + O2 BrO + O2 Br + O2

  25. Wrong Answer! The bromine atom is an intermediate and behaves as both a reactant and a product. Try Again

  26. 2H2O2(l)  2H2O(l) + O2(g) A B N2O4(g)  2NO2(g) C H2(g) + I2(g)  2HI(g) 2NCl3 (g)  N2(g) + 3CI2(g) D Question 13 For which one of the following reactions would pressure measurements be the least sensitive for measuring the initial rate of reaction?

  27. Wrong Answer! Two volumes of gas form two volumes of gas. Hence, there is no change in pressure. Try Again

  28. Increasing the pressure often decreases the rates of reaction involving gases. The smaller the size of the reacting particles, the faster the reaction. A B The rate of a chemical reaction can be decreased by decreasing the temperature. The rates of most chemical reactions derease with time. C D Question 14 All the following statements are correct except

  29. Wrong Answer! Increasing the pressure increases the concentration of reacting gases and hence generally increases the rate of reaction. Try Again

  30. Substituting 1.0 moldm-3 hydrochloric acid for methanoic acid. Substituting powdered magnesium in the place for magnesium turnings. A B Increasing the temperature of the 1.0 moldm-3 methanoic acid at 600C. C Using 300cm3 of the 1.0 moldm-3 methanoic acid instead of 100cm3. D Question 15 When 100cm3 of 1.0 moldm-3 methanoic acid,HCOOH, are added to 1 gram of magnesium turnings at 200C, hydrogen gas is slowly produced. All the following will increase the initial rate of hydrogen production except

  31. Wrong Answer! Tripling the volume of the acid will not alter the initial rate of reaction since there is no change in concentration and hence there will be no effect on the collision rate between magnesium atoms and hydrogen ions from the methanoic acid. Try Again

  32. I only II only A B I and III only III only C D Question 16 When ammonia is manufactured commercially a catalyst is used. What is the effect of this catalyst? N2(g) + 3H2(g) 3NH3(g) ΔH = -92kJ • To shift the position of equilibrium and increase the yield of ammonia. • To increase the rate of only the forward reaction. • To increase the rates of the forward and reverse reactions.

  33. Wrong Answer! A catalyst will increase the rate at which equilibrium is reached, as it will speed up both the forward and reverse reactions equally, but it will have no effect on the position of the equilibrium and hence the value of Kc. Try Again

  34. Congratulations!

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