Which of the following is true about the formation of bonds between molecules?

• Energy is given off when bonds are formed between molecules.

• Energy is absorbed by the molecule when bonds are formed.

• Energy is neither given off nor absorbed when bonds are formed.

• Energy is given off when bonds are broken.

The energy level of molecules will _________ during bond breaking and _________ during bond forming.

• decrease, increase

• increase, increase

• increase, decrease

• decrease, decrease

Which of the following is an application of exothermic reactions

• cold pack

• hot pack

• cooking an egg

• photosynthesis

When the solids Ba(OH)₂ and NH₄SCN are mixed, a solution is produced and the temperature drops. Which statement about the energetics of this reaction is correct?

• The reaction is endothermic and ΔH is negative

• The reaction is endothermic and ΔH is positive

• The reaction is exothermic and ΔH is negative

• The reaction is exothermic and ΔH is positive

The following equation shows the formation of magnesium oxide from magnesium metal. Which statement is correct for this reaction?

2Mg(s) + O₂(g) → 2MgO(s); ΔH = -1204 kJ

• 1204 kJ of energy are released for every mole of magnesium reacted

• 602 kJ of energy are absorbed for every mole of magnesium oxide formed

• 602 kJ of energy are released for every mole of oxygen reacted

• 1204 kJ of energy are released for every two moles of magnesium oxide formed

For the reaction 2H₂(g) + O₂(g) → 2H₂O(g) the bond enthalpies (in kJ/mol) are

H-H = x, O=O = y, O-H = z

Which calculation will give the value, in kJ/mol, of ΔH for the reaction?

• 2x + y - 2z

• 4z - 2x - y

• 2x + y - 4z

• 2z - 2x - y

Using the table of average bond energies below the image, the ΔH for the reaction in kJ is.....

• +160 kJ

• -63 kJ

• -160 kJ

• -217 kJ

Breaking bonds is a/an _______________ process.

• Endothermic

• Exothermic

• Hydrophilic

• Hydrophobic

It takes 631 kJ/mol to break a N=O bond. How much energy is required to make a N=O bond?

• No option is correct

• 402 kJ/mol

• 1262 kJ/mol

• -631 kJ/mol

What is the formula for calculating  $\Delta H$   of a reaction?

•  $\Delta H=H$  (reactants) +  $H$  (products)

•  $\Delta H=H$  (reactants)  - $H$  (products)

•  $\Delta H=H$  (products)  $\div$    $H$  (reactants)

•  $\Delta H=H$  (reactants) x  $H$  (products)

Tags

NGSS.HS-PS1-4