Q: Which of the following is the correct formula for the calculation of the enthalpy change of a reaction using bond enthalpies?

$$\Delta H = \sum \text{(bond enthalpies of bonds broken)} - \sum \text{(bond enthalpies of bonds formed)}$$

Question 1

Which of the following statements best describes why water has a higher boiling point than expected compared to other group 16 hydrides?

Accepted Answer

Water molecules form strong hydrogen bonds due to the high electronegativity of oxygen.

Question 2

A student is asked to calculate the enthalpy change for the combustion of ethanol using the following data: mass of ethanol burned = 0.92 g, temperature rise of water = 20°C, mass of water = 100 g, specific heat capacity of water = $$4.18 \ \mathrm{J} \ \mathrm{g}^{-1} \ ^\circ\mathrm{C}^{-1}. $$What is the enthalpy change per mole of ethanol combusted?

Accepted Answer

$$\Delta H = -1270 \ \mathrm{kJ} \ \mathrm{mol}^{-1}$$

Question 3

Which of the following best explains why sodium chloride conducts electricity when molten but not when solid?

Accepted Answer

Ions are free to move in the molten state but fixed in the solid lattice.

Question 4

A sample of chlorine gas contains two isotopes, $$^{35}\mathrm{Cl} (75$$%) and $$^{37}\mathrm{Cl} (25$$%). What is the relative atomic mass of chlorine?

Accepted Answer

$$35.5$$

Question 5

Which of the following is the correct expression for the equilibrium constant $$K_c$$ for the reaction: $$2\mathrm{NO}_2(g) \rightleftharpoons \mathrm{N}_2\mathrm{O}_4(g)$$?

Accepted Answer

$$K_c = \dfrac{[\mathrm{N}_2\mathrm{O}_4]}{[\mathrm{NO}_2]^2}$$

Question 6

Which of the following statements about the SN1 and SN2 mechanisms for halogenoalkane hydrolysis is correct?

Accepted Answer

SN1 involves a carbocation intermediate and is favored by tertiary halogenoalkanes.

Question 7

A buffer solution is prepared by mixing $$0.10$$ mol of ethanoic acid ($$\mathrm{CH}_3\mathrm{COOH}) $$and $$0.10$$ mol of sodium ethanoate ($$\mathrm{CH}_3\mathrm{COONa}) in$$ $$1.0 dm$^3 of $$solution. Given $$K_a = 1.8 	imes 10$$^{-5}$$ mol dm$$^{-3}$$, what is the pH of the buffer?

Accepted Answer

$$4.74$$

Question 8

Which of the following best describes the role of vanadium(V) oxide ($$\mathrm{V}_2\mathrm{O}_5) in $$the Contact Process for sulfuric acid production?

Accepted Answer

It acts as a heterogeneous catalyst by providing an alternative reaction pathway with lower activation energy.

Question 9

Which of the following compounds will show a strong absorption in the IR spectrum around $$1700 \ \mathrm{cm}^{-1}$$?

Accepted Answer

Propanone ($$\mathrm{CH}_3\mathrm{COCH}_3)$$

Question 10

A student adds aqueous silver nitrate to a solution containing chloride, bromide, and iodide ions. Which sequence of observations is correct as the silver nitrate is added?

Accepted Answer

White precipitate forms first, then cream, then yellow as more silver nitrate is added.

Question 11

Which of the following is the correct order of increasing electronegativity according to the Pauling scale: N, O, F, C?

Accepted Answer

C \u003c N \u003c O \u003c F

Question 12

Which of the following best explains why graphite conducts electricity but diamond does not?

Accepted Answer

Graphite has delocalized electrons between layers, while diamond has all electrons localized in covalent bonds.

Question 13

Which of the following is the correct formula for the calculation of the enthalpy change of a reaction using bond enthalpies?

Accepted Answer

$$\Delta H = \sum 	ext{(bond enthalpies of bonds broken)} - \sum 	ext{(bond enthalpies of bonds formed)}$$

Question 14

Which of the following is a correct statement about the effect of temperature on the value of the equilibrium constant $$K_c$$ for an exothermic reaction?

Accepted Answer

Increasing temperature decreases $$K_c$$ for an exothermic reaction.

Question 15

Which of the following is the best explanation for the color of transition metal complexes?

Accepted Answer

The splitting of d-orbital energy levels by ligands allows absorption of visible light, promoting d-d transitions.

Question 16

A student is asked to prepare a buffer solution with a pH of 5.0 using ethanoic acid ($$pK_a = 4.76) $$and sodium ethanoate. What ratio of $$[\mathrm{CH}_3\mathrm{COO}^-] to$$ $$[\mathrm{CH}_3\mathrm{COOH}] is $$required?

Accepted Answer

$$1.74:1$$

Question 17

Which of the following is a correct statement about the reaction of chlorine with cold, dilute sodium hydroxide?

Accepted Answer

Chlorine undergoes disproportionation to form chloride and chlorate(I) ions.

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