6.2. Rate of reaction
A subsection of Chemistry, 0620, through 6. Chemical reactions
Listing 10 of 319 questions
The equation for the reaction between methanoic acid and ethanol in the presence of a catalyst can be represented as shown. HCOOH + CH3CH2OH X + H2O ∆H = –29.5 kJ / mol X represents the ester formed. In the equation, methanoic acid is represented by the formula HCOOH. Name this type of formula. Write the empirical formula of methanoic acid. Name and draw the displayed formula of ester X. name displayed formula  The reaction is reversible and reaches an equilibrium within a closed system. State what is meant by the term closed system. State two characteristics of an equilibrium.  Complete Table 4.1 to show the effect, if any, on the concentration of X at equilibrium for each change of condition. Table 4.1 change of condition effect on the concentration of X at equilibrium temperature is decreased concentration of HCOOH is decreased concentrations of both HCOOH and CH3CH2OH are decreased the catalyst is removed  
0620_m24_qp_42
THEORY
2024
Paper 4, Variant 2
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For Examiner's Use Enzymes are biological catalysts. They are used both in research laboratories and in industry. Enzymes called proteases can hydrolyse proteins to amino acids. The amino acids can be separated and identified by chromatography. The diagram below shows a typical chromatogram. sample A sample B solvent front initial level of solvent samples are placed on this line The Rf value of a sample = distance travelled by sample distance travelled by solvent front Some Rf values for amino acids are: glutamic acid = 0.4 glycine = 0.5 alanine = 0.7 leucine = 0.9 Identify the two amino acids on the chromatogram. A is B is Explain why the chromatogram must be exposed to a locating agent before Rf values can be measured. For Examiner's Use Measuring Rf values is one way of identifying amino acids on a chromatogram. Suggest another. The synthetic polymer, nylon, has the same linkage as proteins. Draw the structural formula of nylon. Enzymes called carbohydrases can hydrolyse complex carbohydrates to simple sugars which can be represented as OH HO . Draw the structure of a complex carbohydrate. For Examiner's Use Fermentation can be carried out in the apparatus drawn below. After a few days the reaction stops. It has produced a 12% aqueous solution of ethanol. aqueous glucose and yeast allows carbon dioxide to escape but prevents air entering Complete the equation. C6H12O6 + glucose ethanol carbon dioxide Zymase catalyses the anaerobic respiration of glucose. Define the term respiration. Suggest a reason why the reaction stops after a few days. Why is it essential that there is no oxygen in the flask? What technique is used to concentrate the aqueous ethanol?
0620_s05_qp_3
THEORY
2005
Paper 3, Variant 0
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Use The diagram shows a biogas digester. Animal and vegetable waste is fermented by bacteria. The gas produced is a mixture of mainly carbon dioxide and methane. gas gas out gas holder animal and vegetable waste solid residue fermentation chamber State the name given to the energy-releasing process in which organisms use food and produce carbon dioxide. Hydrogen is also produced during the fermentation. The hydrogen reacts with the carbon dioxide to form methane and oxygen. Complete the equation for this reaction. CO2 + 2H2 + Suggest a use for the methane produced in this reaction. Describe the arrangement and motion of the molecules in methane gas. arrangement motion State the name of the homologous series to which methane belongs. Which one of the following compounds belongs to the same homologous series as methane? Tick one box. C2H4 C2H6 CH3OH CH3CO2H Examiner's Use Which one of the following equations A, B, C or D describes fermentation? A CH4 + H2O CO + 3H2 B C6H12O6 + 6O2 6H2O + 6CO2 C C6H12O6 2C2H5OH + 2CO2 D C6H14 C4H10 + C2H4 Many of the reactions occurring in the biogas digester are catalysed by enzymes. Suggest where the enzymes come from. Define the term catalysis. The solid residue from the biogas digester can be used as a fertiliser. State the names of two non-metallic elements found in fertilisers which are needed for plant growth. and
0620_s06_qp_2
THEORY
2006
Paper 2, Variant 0
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Use Catalysts are often used in industry. What do you understand by the term catalyst? Which type of metals often act as catalysts? A student measured the volume of hydrogen gas produced when a few large pieces of zinc reacted with hydrochloric acid of concentration 2.0 mol / dm3. The hydrochloric acid was in excess. The results are given in the table. time / minutes volume of hydrogen / cm3 Plot a graph of volume of hydrogen against time on the axes below. Label the axes. Examiner's Use Copper ions catalyse the reaction between zinc and hydrochloric acid. On the axes above, sketch the line you would expect for the catalysed reaction. Label this line C. Explain why no more hydrogen is given off after 50 minutes. What would happen to the speed of the reaction if small pieces of zinc were used instead of large pieces, the concentration of hydrochloric acid was 1.0 mol / dm3? The equation for this reaction is Zn + 2HCl → ZnCl2 + H2 State the name of the salt formed in this reaction. Describe a test for hydrogen. test result
0620_s07_qp_2
THEORY
2007
Paper 2, Variant 0
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For Examiner's Use 100.4 100.3 100.2 100.1 100.0 mass of flask and contents / grams time / seconds A student used the apparatus shown below to investigate the rate of reaction of calcium carbonate with dilute hydrochloric acid. CaCO3 + 2HCl CaCl2 + CO2 + H2O cotton wool dilute hydrochloric acid calcium carbonate balance 100.4 Use the information in the equation to suggest why the mass of the flask and contents decreases with time. The graph shows how the mass of the flask and its contents changes with time. For Examiner's Use At what time was the reaction just complete? On the graph, mark with an X the point where the speed of reaction was fastest. The student repeated the experiment but altered the concentration of the hydrochloric acid so that it was half the original value. In both experiments calcium carbonate was in excess and all other conditions were kept the same. On the graph on page 10, draw a curve to show how the mass of the flask and contents changes with time when hydrochloric acid of half the concentration was used. How does the speed of this reaction change when the temperature is increased, smaller pieces of calcium carbonate are used? Complete the following sentence using words from the list. combustion expansion large rapid slow small In flour mills there is often the risk of an explosion due to the rapid of the very particles which have a very surface area to react. Cells in plants and animals break down glucose to carbon dioxide and water. glucose + oxygen carbon dioxide + water State the name of this process. In this process enzymes act as catalysts. What do you understand by the term catalyst?
0620_s09_qp_2
THEORY
2009
Paper 2, Variant 0
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