Chem Retake

8/16/2019 Chem Retake

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Chemistry Retake ch 10 & 11

13 Which statements about exothermic and endothermic reactions are correct?1 During an exothermic reaction, heat is given out.2 The temperature of an endothermic reaction goes up because heat is taken in.3 Burning methane in the air is an exothermic reaction.

A 1, 2 and 3B 1 and 2 onlyC 1 and 3 onlyD 2 and 3 only

14 A power station was designed to burn gaseous fuels only. Which two substances could beused?A carbon dioxide and hydrogenB carbon dioxide and 235UC hydrogen and methaneD methane and 235U

D 2 and 3 only

15 The rate of a reaction depends on temperature, concentration, particle size and catalysts.Which statement is not correct?A Catalysts can be used to increase the rate of reaction.B Higher concentration decreases the rate of reaction.C Higher temperature increases the rate of reaction.D Larger particle size decreases the rate of reaction.

16 The diagram shows the change from an anhydrous salt to its hydrated form. forwardreverse

Which statement is correct?A forward reaction requires heat and waterB forward reaction requires water onlyC reverse reaction requires heat and waterD reverse reaction requires water only anhydrous salt 11 D 31 C 12 A 32 B 13 C 33 D 14 C 34 A 15 B 16 B

4 A fuel cell produces electrical energy by the oxidation of a fuel by oxygen.The fuel is usually hydrogen but methane and methanol are two other fuels which may be used. Adiagram of a hydrogen fuel cell is given below.

(a) When the fuel is hydrogen, the only product is water.What additional product would be formed if methane was used?.............................................................................................................................................. [1](b) Write the equation for the chemical reaction that takes place in a hydrogen fuelcell. .............................................................................................................................................. [1](c) (i) At which electrode does oxidation occur? Explain yourchoice. ....................................................................................................................................... [1](ii) Write an ionic equation for the reaction at thiselectrode. ....................................................................................................................................... [2](d) Fuel cells are used to propel cars.

Give two advantages of a fuel cell over a gasoline-fuelled engine..................................................................................................................................................... .............................................................................................................................................. [2]

[Total: 7]


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5 (a)Sodium chlorate(I) decomposes to form sodium chloride and oxygen. The rate of this reaction isvery slow at room temperature provided the sodium chlorate(I) is stored in a dark bottle to preventexposure to light.

2NaClO! 2NaCl + O2The rate of this decomposition can be studied using the following experiment.20 40 60 80 100

oxygen collects in syringesodium chlorate(I) solutionSodium chlorate(I) is placed in the flask and 0.2 g of copper(II) oxide is added. This catalyses thedecomposition of the sodium chlorate(I) and the volume of oxygen collected is measured everyminute. The results are plotted to give a graph of the type shown below.

(ii)Explain why the gradient (slope) of this graph decreases withtime. ............................................................................................................................................. ....................................................................................................................................... [2]


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Cobalt(II) oxide is a more efficient catalyst for this reaction than copper(II) oxide. Sketch, on thegrid, the graph for the reaction catalysed by cobalt(II) oxide.All other conditions were kept constant. [2]

(b)7(iii) What can you deduce from the comment that sodium chlorate(I) has to be shielded fromlight? ............................................................................................................................................. ....................................................................................................................................... [1](iv) Explain, in terms of collisions between particles, why the initial gradient would be steeper if theexperiment was repeated at a higher temperature.............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ....................................................................................................................................... [3]The ions present in aqueous sodium chloride are Na+(aq), Cl –(aq), H+(aq) and OH–(aq).The electrolysis of concentrated aqueous sodium chloride forms three products. They arehydrogen, chlorine and sodium hydroxide.

© UCLES 20140620/33/O/N/14[Turn over(i)Explain how these three products are formed. Give ionic equations for the reactions at theelectrodes.............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ....................................................................................................................................... [4]

If the solution of the electrolyte is stirred, chlorine reacts with sodium hydroxide to form sodiumchlorate(I), sodium chloride and water.Write an equation for this reaction.(ii)

Cl2 + ...NaOH! ..................... + ..................... + .....................[2][Total: 14]

13 When anhydrous copper(II) sulfate is added to water a solution is formed and heat is given out. Which row correctly shows the temperature change and the type of reaction taking place?

ABC


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Chem Retake