measuring enthalpy changes In all the following questions‚ assume that the densities and specific heat capacities of the solutions are the same as pure water i.e. ρ = 1.0 gcm-3 and c = 4.18 Jg-1K-1 1. Zinc will displace copper from copper (II) sulphate solution according to the following equation: CuSO4(aq) + Zn(s) ( Cu(s) + ZnSO4(aq) If an excess of zinc powder is added to 50 cm3 of 1.0 moldm-3 copper(II) sulphate‚ the temperature increases by 6.3 oC. Calculate the enthalpy change
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Measuring the enthalpy change of vaporisation of water You should attempt this part of the activity even if you have not seen the demonstration of the practical. 1. Calculate a value for ∆Hvap for water in KJ mol-1 using the data from the demonstration. Also‚ calculate ∆Hvap from the following data gathered by a student; 8100 J were needed to distil 2.95g of water. a) Explain why the boiling tube was surrounded with expanded polystyrene (or other similar insulation)‚ but the condenser was left
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THERMOCHENISTRY Index 1.0 Introduction | | | | | | | | 1 | 2.0 Enthalpy Changes | | | | | | | 2‚3 | 2.1 The Standard Conditions For Calculating Enthalpy Changes | | | | 3.0 Hess’s Law | | | | | | | | 4‚5 | 3.1 The Applications of Hess’s Law | | | | | | 4.0 Standard Molar Enthalpy Change of Formation‚ ΔHof | | | | 6‚7 | 4.1 The Stability of A Compound | | | | | | | 4.2 Using ΔHof
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Calorimetry 1. How many calories would it take to raise the temperature of 200 g of water 100oC? 2. It takes 23.5 J to raise the temperature of 10.0 g of silver by 10oC. What is the specific heat of silver? 3. A 255 g quantity of gold is heated from 28oC to 100oC. How many joules of energy were used? (specific heat of gold = 0.13 J/goC) 4. What will be the final temperature of 5.00 g of silver at 37oC if it gives off 25.0 J of heat to the surroundings
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TABLE OF CONTENTS 6.1 The Nature of Energy 6.2 Enthalpy and Calorimetry 6.3 Hess’s Law 6.4 Standard Enthalpies of FormaCon 6.5 Present Sources of Energy 6.6 New Energy Sources 30 STANDARD ENTHALPIES OF FORMATION Cgraphite(s) Cdiamond(s) ΔH for this process cannot be obtained by
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closed‚ isolated/insulated systems enthalpy change Molar enthalpy Exothermic changes Endothermic changes Hess’s Law Heat capacity specific heat capacity combustion standard heat of formation standard molar enthalpy of reaction (∆Hcomb‚ ∆Hvap‚ ∆Hsol etc.) Heat flow diagram Potential Energy Diagram 2. The standard molar heat of combustion for benzene C6H6(l) is -6542 kJ/mol. a) Write a thermo chemical equation for the reaction. b) What is the enthalpy change per mole of CO2 (kJ/mol of
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in thermochemistry. Explain each one of them by giving an appropriate example: (a) Standard enthalpy change (b) Exothermic process (c) Endothermic process Define and write an example of thermochemical equation for each of the following terms: (a) Enthalpy of formation (b) Enthalpy of combustion (c) Enthalpy of atomisation (d) Enthalpy of neutralisation (e) Enthalpy of hydration (f) Enthalpy of solution (dissolution) (g) Lattice energy Consider the following reaction: H2(g) + ½ O2(g)
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energy than the reactants Enthalpy changes are normally quoted at standard conditions. Standard conditions are : • 1 atm pressure • 298 K (room temperature or 25oC) • Solutions at 1mol dm-3 • all substances should have their normal state at 298K Standard enthalpy change of formation In an exothermic reaction the ∆H is negative In an endothermic reaction the ∆H is positive When an enthalpy change is measured at standard conditions the symbol is used Eg ∆H The enthalpy of formation of an element
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From the experimental data and through its analysis‚ the enthalpy of combustion for the five alcohols were determined; methanol‚ ethanol‚ propanol‚ butanol‚ and pentanol. As the line of best fit in the graph suggests‚ the enthalpy of combustion increased as the sizes of the molecules increased. This was predicted in the hypothesis and proves it to be correct. As seen on the graph‚ the enthalpy of combustion increases from 140kJ/mol for methanol‚ which has the smallest molecular mass‚ to 530kJ/mol
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exothermic B. is endothermic C. has H > 0 D. both a and c are correct E. both b and c are correct 4. Calculate the heat of vaporization of carbon tetrachloride given that the standard molar enthalpy of formation of liquid carbon tetrachloride is -135.4 kJ/mol and the standard molar enthalpy of formation of gaseous carbon tetrachloride is -102.9 kJ/mol. A. +102.9 kJ/mol B. -32.5 kJ/mol C. +238.2 kJ/mol D. +32.5 kJ/mol E. -238.2 kJ/mol 5. The complete combustion of 1 mole of propane
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