Rates, catalysts and reliable endpoints
הוצג| English | משמעות |
|---|---|
| rate/reɪt/ | קצב |
| activation energy/ˌæktɪˈveɪʃn ˈenədʒi/ | אנרגיית השפעול |
What would explain this observation?
- A faster reaction finishes sooner, but it need not make more product. Rate 速率 and final yield answer different questions.
Build the model
- Reaction rate describes reactant used or product formed per time.
- Higher temperature increases the fraction of collisions with enough energy.
- A catalyst provides an alternative pathway with lower activation energy 活化能.
- activation energy: The minimum energy that particles must have for a reaction to occur.
- rate: Change in a measured quantity per unit time.
Two reactions reach the same final gas volume. Which can still differ?
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
The final volume depends on the amounts reacting, not on how fast they react. Two reactions with the same amounts reach the same final volume even if one is much faster; rate is about time, not about the balanced totals.
Match each technical term to its precise meaning.
רמת קושי 2/5 · 140 מטבעות + בונוס קטן בהשלמה הראשונה היום
Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- A product-time graph has a steeper gradient where rate is larger.
- A tangent estimates instantaneous rate; a secant gives average rate over an interval.
- The final plateau reflects the total collected product under the stated conditions.
In the lab: For gas production, check apparatus for leaks, start timing consistently and record volume at regular intervals. Keep concentration, reactant amount and surface area controlled when changing temperature.
Which two habits make the investigation or model in this case more defensible?
רמת קושי 2/5 · 140 מטבעות + בונוס קטן בהשלמה הראשונה היום
Stating the conditions and assumptions lets others repeat the work exactly, and recording the supporting evidence lets them check the conclusion. Hiding disagreeing results removes the evidence that could challenge a wrong conclusion, and one measurement can never establish a wider claim.
Work from known quantities
- Known: gas volume increases from 10 to 34 cubic centimetres between 20 and 60 s.
- Average rate = change in volume/change in time.
- Rate = (34 - 10)/(60 - 20) = 0.60 cubic centimetres per second.
- This is not necessarily the instantaneous rate at 40 s.
Your turn: A reaction makes 24 cubic centimetres of gas in 40 s. Find average rate.
A reaction makes 24 cubic centimetres of gas in 40 s. Find average rate.
רמת קושי 2/5 · 140 מטבעות + בונוס קטן בהשלמה הראשונה היום
The result is 0.6 cm³/s. Known: 24 cubic centimetres of gas in 40 s. Use average rate = volume / time. Rate = 24/40 = 0.6 cubic centimetres per second. This average over the interval need not equal the instantaneous rate at any moment.
Check the conclusion and its limits
- A catalyst does not change the final equilibrium composition at fixed conditions.
- A mass-loss method cannot detect all reactions, and losing gas through a leak biases a collection experiment.
Not true: A faster reaction always produces a larger final amount of product. Rate measures how quickly product forms, not how much finally forms. The final amount is fixed by the limiting reagent; a catalyst or powder changes only the time taken to reach it.
- Reaction rate describes reactant used or product formed per time.
- A product-time graph has a steeper gradient where rate is larger.
- Watch for: A catalyst does not change the final equilibrium composition at fixed conditions.
Rate measures how quickly product forms, not how much finally forms.
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
True. Rate measures how quickly product forms, not how much finally forms. The final amount is fixed by the limiting reagent; a catalyst or powder changes only the time taken to reach it.
The minimum energy that particles must have for a reaction to occur: write the technical term.
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
activation energy means The minimum energy that particles must have for a reaction to occur.