Question 1

What does activation energy (Ea) represent physically?

Accepted Answer

Activation energy is the minimum kinetic energy that colliding molecules must have, with the correct orientation, to distort their bonds enough to reach the unstable transition state and proceed on to products. It is an energy barrier that exists regardless of whether the overall reaction releases or absorbs energy.

Question 2

What does the Arrhenius equation say?

Accepted Answer

The Arrhenius equation k = A·exp(−Ea/RT) says the rate constant k grows exponentially as temperature T rises or activation energy Ea falls. A is the pre-exponential factor (collision frequency and orientation), R is the gas constant, and the exponential term is the fraction of collisions energetic enough to react.

Question 3

Why does temperature have such a strong effect on reaction rate?

Accepted Answer

A small increase in temperature raises the average molecular speed only modestly, but it disproportionately increases the population of molecules in the energetic tail of the Maxwell-Boltzmann speed distribution that lies above Ea. Because that tail grows exponentially, reaction rate is far more sensitive to temperature than average speed is.

Question 4

What is the pre-exponential factor A?

Accepted Answer

The pre-exponential factor A represents how often molecules collide (collision frequency) multiplied by a steric or orientation factor: molecules must collide with the correct geometric alignment, not just sufficient energy, for the reaction to succeed. A sets the theoretical maximum rate if every collision had enough energy.

Question 5

How do catalysts speed up reactions without changing the overall energy released?

Accepted Answer

A catalyst provides an alternative reaction pathway with a lower activation energy, so a larger fraction of collisions clear the (lower) barrier. It is regenerated at the end of the catalytic cycle and is not consumed, and it does not change the energy of the reactants or products, so ΔH is unaffected.

Question 6

What is the difference between exothermic and endothermic reactions on this diagram?

Accepted Answer

In an exothermic reaction, products sit at a lower potential energy than reactants and net energy is released (ΔH negative). In an endothermic reaction, products sit at a higher potential energy than reactants and net energy is absorbed (ΔH positive). Both still climb over the same transition-state peak.

Question 7

Why is activation energy unrelated to whether a reaction is exothermic or endothermic?

Accepted Answer

Activation energy depends on the height of the transition-state barrier above the reactants, not on the energy difference between reactants and products. Some strongly exothermic reactions, like the combustion of paper, still have a high activation energy and need a spark or match to get started.

Question 8

What is collision theory?

Accepted Answer

Collision theory states that for a reaction to occur, reactant particles must collide with both sufficient energy (at least Ea) and the correct orientation. Raising temperature or concentration increases collision frequency and the fraction of energetic collisions, both of which raise reaction rate.

Question 9

What is the transition state?

Accepted Answer

The transition state (or activated complex) is the fleeting, highest-energy arrangement of atoms at the peak of the reaction coordinate diagram, partway between reactant and product bonding. It is not a stable species; it exists only for the duration of a single molecular vibration.

Question 10

Why do catalytic converters in cars need catalysts?

Accepted Answer

Exhaust gas reactions like CO oxidation have activation energies too high to proceed fast enough at engine operating temperatures. The platinum, palladium, and rhodium catalysts in a catalytic converter provide a lower-Ea surface pathway so pollutants are converted to CO2, N2, and H2O quickly enough to matter.

Question 11

How does enzyme catalysis relate to activation energy?

Accepted Answer

Enzymes are biological catalysts that bind reactants (substrates) in an active site shaped to stabilize the transition state, lowering the effective activation energy for a biochemical reaction by many kilojoules per mole. This lets metabolic reactions proceed fast enough at body temperature to sustain life.

🔥 活化能与碰撞理论 — 反应坐标图

工作原理

常见问题

关于本模拟

🔬 展示内容

🎮 使用方法

💡 你知道吗?

常见问题

What did you find?