Chapter 9 An overview of chemical reaction Chemical reactions happen in nature to produce natural substance, and even living organism Chemical reactions have been used by us to produce millions of substance that do not exist in nature Chemical reactions are the central part of the chemical sciences
Chapter 9 An overview of chemical reaction Chemical reactions happen in nature to produce natural substance, and even living organism. Chemical reactions have been used by us to produce millions of substance that do not exist in nature. Chemical reactions are the central part of the chemical sciences
9. 1 Chemical reactions are represented by chemical equations During a chemical reaction, one or more new compounds are formed as a result of the rearrangement of atoms The chemical reaction can be represented by a chemica/ equation(化学反应式), Which shows the substances about to react, called reactants(反应物),t the left of an arrow that points to the newly formed substances, called products(产物) reactant s products
9.1 Chemical reactions are represented by chemical equations During a chemical reaction, one or more new compounds are formed as a result of the rearrangement of atoms. The chemical reaction can be represented by a chemical equation (化学反应式), which shows the substances about to react, called reactants (反应物), to the left of an arrow that points to the newly formed substances, called products (产物)
Law of mass conservation(质量守恒定律) matter is neither created nor destroyed during a chemical reaction. The finding of oxygen resulted from this law The chemical equation must be balanced(平衡) Two hydrogen molecules One oxygen molecule Two water molecules 2H2 十 2H,O
Law of mass conservation (质量守 恒定律): matter is neither created nor destroyed during a chemical reaction. The finding of oxygen resulted from this law. The chemical equation must be balanced (平衡)
9.2 Chemists use relative masses to count atoms and molecules How to measure a specific number of atoms and molecules? By relative masses or molar mass(摩尔质量). 2H2 2 HO 2 moles 1 mole 2 moles Which is Which is Which is 4 grams 32 grams 36 grams Which is Which is which is 12.04×1023 molecules 6.02×1023 molecules 12.04×1023 molecules
9.2 Chemists use relative masses to count atoms and molecules How to measure a specific number of atoms and molecules? By relative masses or molar mass (摩尔质量). 2H2 + O2 = H2O 2 moles 1 mole 2 moles Which is Which is which is 4 grams 32 grams 36 grams Which is Which is which is 12.04×1023molecules 6.02×1023molecules 12.04×1023molecules
9.3 Reaction rate(反应速率)is influenced by concentration and temperature How fast is a given reaction? Kinetics(动力学) Reaction rate can be determined by how fast the product generates or the reactant disappears time (a) Low concentration of high concentration of products, high roducts. low o Reactants o Products concentration of concentration of reactants reactants
9.3 Reaction rate (反应速率) is influenced by concentration and temperature How fast is a given reaction? Kinetics (动力学) Reaction rate can be determined by how fast the product generates or the reactant disappears. time Low concentration of products, high concentration of reactants high concentration of products, low concentration of reactants Reactants Products
The factors influencing the reaction rate (1). How often do the reactant molecules meet? Concentration! (2). How often do the encountered reactant molecules lead to a reaction? High enough kinetic energy to break the chemical bonds in the reactants, temperature (3 ). Sometimes, electromagnetic fields, such as sunlight, may also lead to reactions Before collision Collision After collision (a)Effective collision 9a9. Before collision Collision After collision (b)Ineffective collision Fig 9.7 during a reaction, reactant molecules collide with each other
The factors influencing the reaction rate: (1). How often do the reactant molecules meet? Concentration! (2). How often do the encountered reactant molecules lead to a reaction? High enough kinetic energy to break the chemical bonds in the reactants, temperature! (3). Sometimes, electromagnetic fields, such as sunlight, may also lead to reactions. Fig 9.7 during a reaction, reactant molecules collide with each other
Broken bonds are a necessary first step in most of chemical reactions. The energy required for this in initial breaking of bonds can be viewed as an energy barrier. The minimum energy required to overcome this energy barrier is known as the activation energy(活化能) H C-N H c H2c一N≡C H 2c一c≡N Reaction pathway
Broken bonds are a necessary first step in most of chemical reactions. The energy required for this in initial breaking of bonds can be viewed as an energy barrier. The minimum energy required to overcome this energy barrier is known as the activation energy (活化能)
At any given temperature, there is a wide distribution of kinetic energies in reactant molecules. When the temperature of reactions is increased the number of reactant molecules having sufficient energy to pass over the barrier also increases, leading to increased reaction speed
At any given temperature, there is a wide distribution of kinetic energies in reactant molecules. When the temperature of reactions is increased, the number of reactant molecules having sufficient energy to pass over the barrier also increases, leading to increased reaction speed
94 Catalysts(催化剂) increase the rate of chemical reactions a third way to increase the rate of a reaction is to add a catalyst, which is any substance that increases the rate of a chemical reaction by lowing its activation energy. The catalyst may participate as a reactant, but it is then regenerated as a product Uncatalyzed rea reaction 20 H O.+2H.o+B 2Br +2H Reaction pathway
9.4 Catalysts (催化剂) increase the rate of chemical reactions • A third way to increase the rate of a reaction is to add a catalyst, which is any substance that increases the rate of a chemical reaction by lowing its activation energy. The catalyst may participate as a reactant, but it is then regenerated as a product
C|+O3 CIO+O2 C|o+O3一C}+O2 One chlorine atom in the ozone layer can catalyze the transformation of 100,000 ozone molecules to oxygen molecules in one or two years
• Cl + O3 ClO + O2 • ClO + O3 Cl + O2 • One chlorine atom in the ozone layer can catalyze the transformation of 100,000 ozone molecules to oxygen molecules in one or two years