Take this Exam: GCSE Chemistry: Energy Changes | Zestly

Question 1

Why is the combustion of fuels like methane considered an exothermic reaction?

Accepted Answer

Because more energy is released forming bonds in products than is needed to break bonds in reactants.

Question 2

On a reaction profile diagram, what does the 'hump' or peak represent?

Accepted Answer

The activation energy.

Question 3

If a reaction has an overall energy change of $-100 	ext{ kJ/mol}$, which of the following is true?

Accepted Answer

The reaction is exothermic.

Question 4

Which of the following correctly identifies the function of a hand warmer?

Answer

It uses an exothermic reaction to release heat.

Answer

It uses an endothermic reaction to absorb heat.

Answer

It uses a catalyst to lower the activation energy.

Answer

It uses a physical change to store energy.

Question 5

Calculate the energy change for the reaction N2 + 3H2 → 2NH3. Bond energies: N≡N = 945 kJ/mol, H–H = 436 kJ/mol, N–H = 391 kJ/mol. (Each NH3 molecule contains three N–H bonds.)

Answer

+93 kJ/mol

Answer

−93 kJ/mol

Answer

+105 kJ/mol

Answer

−105 kJ/mol