Fig. 1 shows an energy profile prepared by a resin manufacturer. The reaction joins small carbon-containing molecules to make a tough coating for metal tool...
Question 1 Report
Fig. 1 shows an energy profile prepared by a resin manufacturer. The reaction joins small carbon-containing molecules to make a tough coating for metal tools. The reaction begins with reactants at 120 kJ and forms products at 70 kJ. The highest point on the uncatalysed pathway is 210 kJ. A catalyst gives a second route whose highest point is 155 kJ. The company needs a rapid reaction at a lower temperature so that less energy is used. The catalyst is not used up during the reaction.
(a) Give the activation energy for the uncatalysed reaction. [2]
(b) Use Fig. 1 to calculate the energy change for the reaction. [3]
(c) Describe whether the reaction is exothermic or endothermic. Use the energy values in Fig. 1. [3]
(d) Give the activation energy when the catalyst is used and calculate the decrease in activation energy. [4]
(e) Describe how a catalyst allows the manufacturer to save energy during production. [4]
Answer Details
Energy profiles and catalysts
- (a) Activation energy for the uncatalysed pathway: \[210-120=\mathbf{90\text{ kJ}}\] [2]
- (b) Energy change: \[70-120=\mathbf{-50\text{ kJ}}\] The energy change is −50 kJ, meaning 50 kJ is released. [3]
- (c) The reaction is exothermic. Products are at lower energy than reactants, 70 kJ compared with 120 kJ, so 50 kJ is released. [3]
- (d) Catalysed activation energy: \[155-120=35\text{ kJ}\] Decrease in activation energy: \[90-35=\mathbf{55\text{ kJ}}\] [4]
- (e) A catalyst provides an alternative pathway with lower activation energy. More particles therefore react successfully at a lower temperature, so less heating energy is needed. The catalyst is not used up. [4]
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