People's Education Press High School Chemistry - Compulsory Course, Volume 2: Multidimensional Perspectives on Chemical Reactions: Energy, Rate, and Extent

Welcome to the 'multidimensional space' of chemistry. In past studies, we often focused only on matter transformation—i.e., 'who turned into whom.' True chemical thinking requires us to establish athree-dimensional evaluation system:energy change (heat and electricity), reaction rate (fast and slow), and reaction extent (deep and shallow).

Core Theorems and Fundamentals

Theorem and Derivation: When a chemical reaction occurs, breaking bonds in reactants absorbs energy, while forming bonds in products releases energy. This 'net energy difference' determines the reaction’s macroscopic thermal effect.

Microscopic Essence: Bond breaking and formation are the root cause of energy fluctuations.
Energy Transformation: Chemical energy can be converted not only into thermal energy (e.g., combustion) but also into electrical energy under specific conditions (e.g., in batteries).
Multidimensional Coordination: For example, in industrial ammonia synthesis, we use catalysts to increaserate, adjustextent, and properly manage the releasedEnergy.

⚠️ Common Pitfall

Energy change necessarily accompanies a chemical reaction is a flawed logic. Physical changes (e.g., light emission from a bulb, melting ice) also involve significant energy transformation. The sole criterion for identifying a chemical reaction remains: 'Is a new substance formed?'

QUESTION 1

The essence of a chemical reaction is the formation of new substances. Matter transformation is one fundamental characteristic. Another fundamental characteristic is ______, typically manifested as the release or absorption of ______.

energy change; heat

atomic reorganization; light energy

bond breaking; electrical energy

QUESTION 2

In chemical industry production, merely knowing what substances are produced is insufficient. Based on the 'multidimensional perspective' discussed in this lesson, briefly explain why engineers must consider both reaction rate and extent simultaneously when designing production processes?

Rate determines efficiency; extent determines yield/conversion rate

Only fast rates ensure complete reaction

QUESTION 3

A student observed that the beaker wall became very cold during the reaction between barium hydroxide crystals and ammonium chloride solid. Explain, from the perspective of microscopic chemical bonds, why this reaction appears to absorb heat, and describe how energy is transformed in this process.

Bond breaking absorbs more energy than bond forming releases; thermal energy is converted into chemical energy

Bond breaking releases less energy than bond forming absorbs; chemical energy is converted into thermal energy

QUESTION 4

In a sealed container under certain conditions, the reversible reaction $N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)$ occurs. Which of the following situations cannot indicate that the reaction has definitely reached chemical equilibrium? ( )

The concentrations of $N_2$, $H_2$, and $NH_3$ no longer change

One mole of $N_2$ is generated per unit time while three moles of $H_2$ are consumed

The pressure of the gas inside the container no longer changes

One mole of $N_2$ is consumed per unit time while three moles of $H_2$ are consumed

QUESTION 5

Which of the following statements about energy changes in chemical reactions is correct?

All reactions requiring heating to occur are endothermic

In a chemical reaction, if the energy absorbed in breaking bonds is less than the energy released in forming bonds, the reaction is exothermic

Chemical reactions inevitably involve heat changes, and energy forms can only be thermal energy