Chapter 20
暂无描述。系统推荐的高质量记忆内容，适合每天坚持背诵学习。
卡片预览 (15 张)
Elements that Don’t react at all
He, Ne
Elements that are Very reactive
Most alkali metals Li, Na, K, Rb, Cs Halogens F, Cl, Br, I
Molecular Orbitals & Bonding
When atoms get close, MO’s can form If the electrons are lower in energy in the resulting MO’s than they were in the atomic orbitals, bonds form
Conservation of Matter: Balancing Chemical Reactions
Matter is not created or destroyed in chemical reactions This is reflected in the way we write them Matter is not created or destroyed in chemical reactions This is reflected in the way we write them Count the atoms! 2H2 + O2 2H2O 2Mg + O2 2MgO
What Governs Speed of a Reaction?
Factors that impact Rate: Physical state of reactants Collision rate (increases with temp) Energetic requirements (temp) Entropy (organization) requirements
Reaction Rate
rate that reactants are consumed, or products are produced
Examples of Cellulose
Dead tree in forest Wood in fire Sawdust in explosion
What controls collision rate?
Temperature (because it is a reflection of molecular speed) Physical state (reactants collide more often in gas or liquid states) Pressure (for gases) or concentration (for liquids)
Effect of Energy
The net energy released (or consumed) does not affect rates The energy required to reach the transition state (“activation energy”) has large effect
Transition State
The critical arrangement of atoms where the reacting system “decides” whether or not to make products Typically involves breaking and/or formation of bonds
Thermite
Very large energy release (molten Fe)! Only goes with hot fuse (requires high activation energy) Raise the screen to do this!
Effect of Entropy
Reactants frequently must have a certain orientation at the transition state, or reaction will not occur This corresponds to order in the transition state: entropy of activation
Catalysts
Decrease energy of activation without themselves being consumed; speed up rate H2O2 decomposes spontaneously Much faster in presence of or MnO2 Catalyst makes new, lower energy route possible`
Equilibrium
Reactions go in both directions: Reactants Products You’ve already seen this in the H2 + O2 reaction This dynamic balance is called “chemical equlibrium”`
Meaning of Equilibrium
When forward and reverse rates are equal, amount of reactant & product no longer changes Equilibrium is the state of lowest energy and maximum entropy; everything moves toward it