The minimum amount of energy which the reactant particles must possess for a collision to result in a reaction.
打一個(gè)比方，我們?cè)隈{駛汽車的時(shí)候，首先要將汽車點(diǎn)火，這就需要一定的能量。同樣地，一個(gè)化學(xué)反應(yīng)想要發(fā)生，也需要一定的能量來啟動(dòng)，這個(gè)能量就是活化能。如下圖所示，活化能 Ea 是過渡態(tài)的能量和反應(yīng)物的能量的差值。
02
答案：C
解析 ??這道題考察的是Factors affecting the rate of reaction。Factors affecting the rate of reaction 有以下三個(gè)：
滿分回答：Decreasing the particle size of the solid will increase the fraction of particles available for collision, increasing frequency of effective collision & hence the rate of reaction.
2. Concentration/Pressure of liquid & gaseous reactants
滿分回答：Increasing the concentration of a reactant (or the pressure of a gaseous reactant) will increase the number of particles in a unit volume. This will increase the frequency of effective collisions & hence the rate of reaction.
3．Temperature
滿分回答：
When the temperature(T) increases, the reactant particles gain kinetic energy(KE).
The frequency of collision increases and the fraction of particles possessing energy equal or greater than the activation energy increases.
This results in an increase in the frequency of effective collisions between time.
Hence, rate of reaction increases.
Note: “frequency of collision & particles with rate of reaction” is required.
03
答案：B
解析 ??這道題考察的是 Catalyst。
Catalyst 定義：
A catalyst is a substance that increases the rate of a chemical reaction without being chemically changed at the end of reaction.
Catalyst can make activation energy decreased.Maxwell-Boltzmann energy distribution curve. 滿分回答：Adding a catalyst decreases the activation energy of a reaction. Hence, the fraction of particles possessing energy equal or greater than the activation energy increases. This results in an increase in the frequency of effective collisions between time.
04
答案：A
解析 ??首先，一定要記住，catalyst 只能改變 activation energy，不改變 enthalpy change。所以，enthalpy change 還是 z，而 activation energy 從原來的 y+z 變成 x+z。Using a Maxwell Boltzmann distribution curve, explain how increasing the temperature increases the rate of reaction.解析 ??綜上所述，IB化學(xué)非常注重基礎(chǔ)概念的熟練程度，主要體現(xiàn)在題目更長(zhǎng)、數(shù)量更多、跨度更大、細(xì)節(jié)更多、計(jì)算量更大等方面。在備考過程中，一定要注意通過基礎(chǔ)題目的練習(xí)，增強(qiáng)自身對(duì)基礎(chǔ)概念的靈活應(yīng)用。由于在整個(gè)考試過程中，不允許使用計(jì)算器，所以學(xué)生也要注意提升自己的計(jì)算能力。
