IB Chemistry Chapter 5

An equation for a reaction in which hydrogen is formed is CH4 + H2O → 3H2 + CO ΔHӨ = +210 kJ Which energy change occurs when 1 mol of hydrogen is formed in this reaction? A. 70 kJ of energy are absorbed from the surroundings. B. 70 kJ of energy are released to the surroundings. C. 210 kJ of energy are absorbed from the surroundings. D. 210 kJ of energy are released to the surroundings.

A

Approximate values of the average bond enthalpies, in kJ mol-1, of three substances are: H-H 430 F-F 155 H-F 565 What is the enthalpy change, in kJ, for this reaction? 2HF → H2 + F2 A. +545 B. +20 C. -20 D. -545

A

Consider the following reactions. S(s) + O2(g) → SO3(g) ΔHӨ = −395 kJ mol−1 SO2(s) + O2(g) → SO3(g) ΔHӨ = −98 kJ mol−1 What is the ΔHӨ value (in kJ mol-1) for the following reaction? S(s) + O2(g) → SO2(g) A. -297 B. +297 C. - 493 D. +493

A

The average bond enthalpies for O—O and O==O are 146 and 496 kJ mol-1 respectively. What is the enthalpy change, in kJ, for the reaction below? H—O—O—H(g) → H—O—H(g) + ½O==O(g) A. - 102 B. + 102 C. + 350 D. + 394

A

The mass m (in g) of a substance of specific heat capacity c (in J g-1 K-1 ) increases by t°C. What is the heat change in J? A. mct B. mc(t + 273) C. D.

A

Using the equations below Cu(s) + O2(g) → CuO(s)∆Hο = -156 kJ 2Cu(s) + O2(g) → Cu2O(s)∆Hο = -170 kJ what is the value of ∆Hο (in kJ) for the following reaction? 2CuO(s) → Cu2O(s) + O2(g) A. 142 B. 15 C. -15 D. -142

A

When 40 joules of heat are added to a sample of solid H2O at -16.0°C the temperature increases to -8.0°C. What is the mass of the solid H2O sample? [Specific heat capacity of H2O(s) = 2.0 J g-1K-1] A. 2.5 g B. 5.0 g C. 10 g D. 160 g

A

Which statements are correct for all exothermic reactions? I. The enthalpy of the products is less than the enthalpy of the reactants. II. The sign of ΔH is negative. III. The reaction is rapid at room temperature. A. I and II only B. I and III only C. II and III only D. I, II and III

A

Which statements are correct for an endothermic reaction? I. The system absorbs heat. II. The enthalpy change is positive. III. The bond enthalpy total for the reactants is greater than for the products. A. I and II only B. I and III only C. II and III only D. I, II and III

A

A sample of a metal is heated. Which of the following are needed to calculate the heat absorbed by the sample? I. The mass of the sample II. The density of the sample III. The specific heat capacity of the sample A. I and II only B. I and III only C. II and III only D. I, II and III

B

A simple calorimeter was used to determine the enthalpy of combustion of ethanol. The experimental value obtained was -920 kJ mol-1. The Data Booklet value is -1371 kJ mol-1. Which of the following best explains the difference between the two values? A. incomplete combustion of the fuel B. heat loss to the surroundings C. poor ventilation in the laboratory D. inaccurate temperature measurements

B

According to the enthalpy level diagram below, what is the sign for ΔH and what term is used to refer to the reaction? ΔH reaction A. positive endothermic B. negative exothermic C. positive exothermic D. negative endothermic

B

Separate solutions of HCl(aq) and H2SO4(aq) of the same concentration and same volume were completely neutralized by NaOH(aq). X kJ and Y kJ of heat were evolved respectively. Which statement is correct? A. X = Y B. Y = 2X C. X = 2Y D. Y = 3X

B

Using the equations below: C(s) + O2(g) → CO2(g) ∆H = -390 kJ Mn(s) + O2(g) → MnO2(s) ∆H = -520 kJ what is ∆H (in kJ) for the following reaction? MnO2(s) + C(s) → Mn(s) + CO2(g) A. 910 B. 130 C. -130 D. -910

B

Using the equations below: C(s) + O2(g) → CO2(g) ∆Hο = -394 kJ mol-1 Mn(s) + O2(g) → MnO2(s) ∆Hο = -520 kJ mol-1 What is ∆H, in kJ, for the following reaction? MnO2(s) + C(s) → Mn(s) + CO2(g) A. 914 B. 126 C. -126 D. -914

B

When the solids Ba(OH)2 and NH4SCN are mixed, a solution is produced and the temperature drops. Ba(OH)2(s) + 2NH4SCN(s) → Ba(SCN)2(aq) + 2NH3(g) + 2H2O(l) Which statement about the energetics of this reaction is correct? A. The reaction is endothermic and ΔH is negative. B. The reaction is endothermic and ΔH is positive. C. The reaction is exothermic and ΔH is negative. D. The reaction is exothermic and ΔH is positive.

B

Which statement is correct for an endothermic reaction? A. Bonds in the products are stronger than the bonds in the reactants. B. Bonds in the reactants are stronger than the bonds in the products. C. The enthalpy of the products is less than that of the reactants. D. The reaction is spontaneous at low temperatures but becomes non-spontaneous at high temperatures.

B

Consider the following equations. Mg(s) + O2(g) → MgO(s) ∆Hο = -602 kJ H2(g) + O2(g) → H2O(g) ∆Hο = -242 kJ What is the ∆H° value (in kJ) for the following reaction? MgO(s) + H2(g) → Mg(s) + H2O(g) A. -844 B. -360 C. +360 D. +844

C

Consider the specific heat capacity of the following metals. Metal Specific heat capacity / J kg-1 K-1 Cu 385 Ag 234 Au 130 Pt 134 Which metal will show the greatest temperature increase if 50 J of heat is supplied to a 0.001 kg sample of each metal at the same initial temperature? A. Cu B. Ag C. Au D. Pt

C

For the reaction 2H2(g) + O2(g) → 2H2O(g) the bond enthalpies (in kJ mol-1) are H-H x O=O y O-H z Which calculation will give the value, in kJ mol-1, of ΔHӨ for the reaction? A. 2x + y -2z B. 4z - 2x - y C. 2x + y - 4z D. 2z -2x - y

C

How much energy, in joules, is required to increase the temperature of 2.0 g of aluminium from 25 to 30°C? (Specific heat of Al = 0.90 J g-1 K-1). A. 0.36 B. 4.5 C. 9.0 D. 54

C

The following equations show the oxidation of carbon and carbon monoxide to carbon dioxide. C(s) +O2(g) → CO2(g) ΔHӨ = -x kJ mol-1 CO(g) + O2(g)→ CO2(g) ΔHӨ = -y kJ mol-l What is the enthalpy change, in kJ mol-1, for the oxidation of carbon to carbon monoxide? C(s) + O2(g)→ CO(g) A. x + y B. - x - y C. y - x D. x - y

C

The standard enthalpy change of formation values of two oxides of phosphorus are: P4(s) + 3O2(g) → P4O6(s) ΔHӨf= -1600 kJ mol-1 P4(s) + 5O2(g) → P4O10(s) ΔHӨf= -3000 kJ mol-1 What is the enthalpy change, in kJ mol-1, for the reaction below? P4O6(s) + 2O2(g) → P4O10(s) A. +4600 B. +1400 C. -1400 D. -4600

C

The temperature of a 2.0 g sample of aluminium increases from 25°C to 30°C. How many joules of heat energy were added? (Specific heat of Al = 0.90 J g-1K-1) A. 0.36 B. 2.3 C. 9.0 D. 11

C

Which combination is correct for a chemical reaction that absorbs heat from the surroundings? Type of reaction ΔH at constant pressure A. Exothermic Positive B. Exothermic Negative C. Endothermic Positive D. Endothermic Negative

C

Which of the quantities in the enthalpy level diagram below is (are) affected by the use of a catalyst? Time A. I only B. III only C. I and II only D. II and III only

C

Which statement about bond enthalpies is correct? A. Bond enthalpies have positive values for strong bonds and negative values for weak bonds. B. Bond enthalpy values are greater for ionic bonds than for covalent bonds. C. Bond breaking is endothermic and bond making is exothermic. D. The carbon-carbon bond enthalpy values are the same in ethane and ethene.

C

Which statement is correct about the reaction shown? 2SO2(g) + O2(g) → 2SO3(g) ΔH = -196 kJ A. 196 kJ of energy are released for every mole of SO2(g) reacted. B. 196 kJ of energy are absorbed for every mole of SO2(g) reacted. C. 98 kJ of energy are released for every mole of SO2(g) reacted. D. 98 kJ of energy are absorbed for every mole of SO2(g) reacted.

C

Which statement is correct for an endothermic reaction? A. The products are more stable than the reactants and ΔH is positive. B. The products are less stable than the reactants and ΔH is negative. C. The reactants are more stable than the products and ΔH is positive. D. The reactants are less stable than the products and ΔH is negative.

C

For which of the following is the sign of the enthalpy change different from the other three? A. CaCO3(s) → CaO(s) + CO2(g) B. Na(g) → Na+(g) + e- C. CO2(s) → CO2(g) D. 2Cl(g) → Cl2(g)

D

The average bond enthalpy for the C―H bond is 412 kJ mol-1. Which process has an enthalpy change closest to this value? A. CH4(g) → C(s) + 2H2(g) B. CH4(g) → C(g) + 2H2(g) C. CH4(g) → C(s) + 4H(g) D. CH4(g) → CH3(g) + H(g)

D

The equations and enthalpy changes for two reactions used in the manufacture of sulfuric acid are: S(s) O2(g) → SO2(g) ΔHӨ = -300 kJ 2SO2(g) + O2(g) → 2SO3(g) ΔHӨ = -200 kJ What is the enthalpy change, in kJ, for the reaction below? 2S(s) + 3O2(g) → 2SO3(g) A. -100 B. -400 C. -500 D. -800

D

The following equation shows the formation of magnesium oxide from magnesium metal. 2Mg(s) + O2(g)→2MgO(s) ΔHӨ = -1204kJ Which statement is correct for this reaction? A. 1204 kJ of energy are released for every mol of magnesium reacted. B. 602 kJ of energy are absorbed for every mol of magnesium oxide formed. C. 602 kJ of energy are released for every mol of oxygen gas reacted. D. 1204 kJ of energy are released for every two mol of magnesium oxide formed.

D

The ΔHӨ values for the formation of two oxides of nitrogen are given below. N2(g) + O2(g) → NO2(g) ΔHӨ = -57 kJ mol-1 N2(g) + 2O2(g) → N2O4(g) ΔHӨ = +9 kJ mol-1 Use these values to calculate ΔHӨ for the following reaction (in kJ): 2NO2(g) → N2O4(g) A. -105 B. - 48 C. +66 D. +123

D

What energy changes occur when chemical bonds are formed and broken? A. Energy is absorbed when bonds are formed and when they are broken. B. Energy is released when bonds are formed and when they are broken. C. Energy is absorbed when bonds are formed and released when they are broken. D. Energy is released when bonds are formed and absorbed when they are broken.

D

Which statements about exothermic reactions are correct? I. They have negative ΔH values. II. The products have a lower enthalpy than the reactants. III. The products are more energetically stable than the reactants. A. I and II only B. I and III only C. II and III only D. I, II and III

D