Catalysts: a lower barrier, the same overall energy change
| English | 中文 | Pinyin |
|---|---|---|
| catalyst/ˈkætəlɪst/ | 催化剂 | cuī huà jì |
| catalysed pathway | 催化反应路径 | cuī huà fǎn yìng lù jìng |
What would explain this observation?
- A catalyst 催化剂 lets a reaction proceed faster without appearing as a consumed reactant in the overall equation. It changes the route, not the identities of the starting and finishing substances.
- Start with a prediction. State the quantities or features you would compare, then decide what evidence could distinguish two explanations.
Build the model
- Catalysts increase reaction rate by providing a different reaction pathway with a lower activation energy. They are not used up overall, although they may participate in steps and be regenerated. Different reactions need different catalysts; enzymes act as catalysts in biological systems. On a reaction profile, the catalysed curve has a lower peak but the same reactant and product levels as the uncatalysed curve. The overall energy change is therefore unchanged.
- catalyst: A substance increasing reaction rate by a lower-activation pathway without being used up overall; catalysed pathway 催化反应路径: An alternative reaction route with a lower activation barrier.
Which feature changes on the profile when a suitable catalyst is added?
At the same temperature more colliding particles can meet the smaller activation requirement. This does not mean the catalyst adds energy to every particle or increases temperature by definition. Evidence for catalytic behaviour combines rate increase and regeneration/no net consumption. An unchanged small sample alone does not prove catalysis unless the reaction-rate effect is shown. The overall equation omits a regenerated catalyst from its stoichiometric reactant and product lists.
Match each technical term to its precise meaning.
Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- At the same temperature more colliding particles can meet the smaller activation requirement. This does not mean the catalyst adds energy to every particle or increases temperature by definition. Evidence for catalytic behaviour combines rate increase and regeneration/no net consumption. An unchanged small sample alone does not prove catalysis unless the reaction-rate effect is shown. The overall equation omits a regenerated catalyst from its stoichiometric reactant and product lists.
- Compare teacher-approved catalysed and uncatalysed trials with matching reactant quantities, concentrations, temperature and collection apparatus. Record time-dependent product measurements rather than only final volume. Use the specified catalysts in the course where required; do not memorise unrelated industrial names. Actual hydrogen peroxide catalyst demonstrations need the school’s selected dilute solutions and protection because rapid gas evolution and warming can occur.
Which two habits make the investigation or model in this case more defensible?
Compare teacher-approved catalysed and uncatalysed trials with matching reactant quantities, concentrations, temperature and collection apparatus. Record time-dependent product measurements rather than only final volume. Use the specified catalysts in the course where required; do not memorise unrelated industrial names. Actual hydrogen peroxide catalyst demonstrations need the school’s selected dilute solutions and protection because rapid gas evolution and warming can occur.
Work from known quantities
- State the known values and their units. Choose the relation because its assumptions fit this case, then rearrange before substitution.
- Known: a supplied profile has reactants at 20, products at 5 and uncatalysed peak at 80 relative units. A catalysed peak is 50. Both paths decrease overall by 15 units; the barriers are visibly different. A fixed endpoint reached in 60 s without catalyst and 20 s with it gives a threefold ratio of mean rates to that endpoint, assuming the same measured amount.
The same fixed endpoint takes 72 s without catalyst and 24 s with it. Find the factor increase in mean rate. Use the same sequence: known quantities → model → relation → substitution → unit and interpretation.
The same fixed endpoint takes 72 s without catalyst and 24 s with it. Find the factor increase in mean rate.
The result is 3 . Known: a supplied profile has reactants at 20, products at 5 and uncatalysed peak at 80 relative units. A catalysed peak is 50. Both paths decrease overall by 15 units; the barriers are visibly different. A fixed endpoint reached in 60 s without catalyst and 20 s with it gives a threefold ratio of mean rates to that endpoint, assuming the same measured amount.
Check the conclusion and its limits
- Do not lower the product energy when drawing the catalysed path or describe the catalyst as consumed in the overall reaction. A catalyst does not increase the fixed limiting-reactant amount of product. At equilibrium it speeds both directions without changing the final composition under fixed conditions; this statement does not require equilibrium-constant calculations.
- Return to the original observation. Explain what the result supports, which conditions it assumes, and one way to test a competing explanation.
A catalyst must be consumed as a reactant in the overall equation. This claim is false: Do not lower the product energy when drawing the catalysed path or describe the catalyst as consumed in the overall reaction. A catalyst does not increase the fixed limiting-reactant amount of product. At equilibrium it speeds both directions without changing the final composition under fixed conditions; this statement does not require equilibrium-constant calculations.
Catalysts: a lower barrier, the same overall energy change: At the same temperature more colliding particles can meet the smaller activation requirement. This does not mean the catalyst adds energy to every particle or increases temperature by definition. Evidence for catalytic behaviour combines rate increase and regeneration/no net consumption. An unchanged small sample alone does not prove catalysis unless the reaction-rate effect is shown. The overall equation omits a regenerated catalyst from its stoichiometric reactant and product lists.
A catalyst must be consumed as a reactant in the overall equation.
Do not lower the product energy when drawing the catalysed path or describe the catalyst as consumed in the overall reaction. A catalyst does not increase the fixed limiting-reactant amount of product. At equilibrium it speeds both directions without changing the final composition under fixed conditions; this statement does not require equilibrium-constant calculations.
A substance increasing reaction rate by a lower-activation pathway without being used up overall: write the technical term.
catalyst means A substance increasing reaction rate by a lower-activation pathway without being used up overall.