Unit 4 - lesson 2

The chemical eqation for the decomposition of magnesium carbonate is as follows :

MgCO_3(s) + 117 KJ = MgO_(s) + CO_2(g)

Based on this chemical equation. Which of this statement is true ?

• 1. 117 kJ of energy is released when a single molecule of MgCO₃ decomposes.

• 2. 117 kJ of energy is released when 1 mole of MgCO₃ decompose.

• 3. 117 kJ of energy is needed to make 1 mole of MgCO₃ decompose.

• 4. 117 kJ of energy is needed to make 42 g of MgCO₃ decompose

• 5. 117 kJ of energy is needed to make a single molecule of MgCO₃ decompose.

The value of Δ𝐻 when liquid water freezes to solid water is −6.01 kJ/mol.What is the value of Δ𝐻 when solid water melts to liquid water? ………………… KJ

• (+3.01)

• (+6.01)

• (+4.01)

• (+12.01)

The chemical equation for the combustion of glucose is shown:

C₆H₁₂O_6(s) + 6O_2(g) = 6CO_2(g) + 6H₂O_(l) + 2808 KJ

How much energy is released when 2.5 moles of glucose are burned?……………… KJ

• 4352

• 7020

• 2808

• 2332

The symbol for standard enthalpy change is Δ𝐻°.

Which of the following is not a standard condition?

• 1. A volume of 1 m³

• 2. A pressure of 1 bar for gases

• 3. All components in their standard state

• 4. A concentration of 1 mol/dm³ for solutions

The molar bond energy of F₂ is 159 kJ/mol.Calculate the energy of one F-F bond.

• 1. 1.65 x 10^-19 J

• 2. 2.64 x 10^-19 J

• 3. 9.58 x 10^-19 J

• 4. 3.78 x 10^-19 J

• 5. 2.55 x 10^-19 J

3.70 mol of Cl-Cl bonds release 888 kJ of energy when they form. How much energy is released when 1000 Cl-Cl bonds form?

• 1. 3.99 x 10^-16 J

• 2. 1.48 x 10^-15 J

• 3. 3.99 X 10^-19 J

• 4. 1.48 X 10^-18 J

• 5. 4.01 X 10^-17 J

Which of the following quantities of bonds requires the most energy to break?

• 1. 5.8 mol I-I (148 KJ/mol)

• 2. 1.0 mol (835 KJ/mol)

• 3. 2.0 mol H-Cl ( 428 KJ/mol)

• 4. 2.0 mol H-H (436 KJ/mol)

• 5. 1.7 mol O=O (494 KJ/mol)

Which of the following are units for the molar enthalpy change of a reaction, Δ𝐻?

• 1. mol/dm³

• 2. ^∘C/atom

• 3. kJ/mol

• 4. cm³/s

• 5. g/mol

A student is setting up an experiment to measure the enthalpy change in a neutralization reaction between hydrochloric acid and potassium hydroxide. Before mixing the two solutions together in a polystyrene cup, the student places a beaker of each solution in a water bath set to 25^oC .Why does the student do this?

• 1. To ensure the reactants have the correct activation energy needed to react

• 2. To make the solutions less viscous

• 3. To ensure both solutions are at the same temperature as each other

• 4. To increase the rate of reaction between the hydrochloric acid and the potassium hydroxide

• 5. To remove any impurities in the solutions

Which of the following is the best definition of an endothermic reaction?

• 1. A reaction that gives out heat

• 2. A reaction that is accelerated by heating

• 3. A reaction that is accelerated by cooling

• 4. A reaction that is spontaneous

• 5. A reaction that absorbs heat