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75 Terms
Activation Energy (Ea)
The minimum energy that reacting particles must have for a reaction to occur
Enthalpy Change (ΔH)
The difference in energy between the reactants and the products in a chemical reaction
Exothermic Reaction
A chemical reaction in which energy is released to the surroundings and the energy of the products is less than that of the reactants
Endothermic Reaction
A chemical reaction in which energy is absorbed from the surroundings and the energy of the products is greater than that of the reactants
Activated Complex
An unstable
Bond Energy
The energy required to break a chemical bond between atoms in a molecule
Rate of Reaction
The change in concentration of reactants or products per unit time
Collision Theory
A theory that explains that chemical reactions occur when particles collide with sufficient energy and correct orientation
Effective Collision
A collision between particles that results in a chemical reaction because the particles have sufficient energy and correct orientation
Catalyst
A substance that increases the rate of a chemical reaction by providing an alternative pathway with a lower activation energy and is not used up in the reaction
Concentration
The amount of substance present in a given volume
Surface Area
The total area of the surface of a solid substance that is exposed
Temperature
A measure of the average kinetic energy of the particles in a substance
Maxwell-Boltzmann Distribution
A graph that shows the distribution of energies among particles in a substance at a given temperature
Reaction Rate (Experimental)
The speed at which reactants are converted into products measured as a change in a measurable quantity over time
Energy Changes in Bonds
Bond breaking requires energy and bond formation releases energy
Successful Collision
A collision that leads to a reaction because particles have enough energy and the correct orientation
Frequency of Collisions
The number of collisions between particles per unit time
Kinetic Energy
The energy that particles have due to their motion
Potential Energy (Chemical)
The energy stored in the chemical bonds of a substance
Heat
The transfer of energy from a hotter object to a colder object
System
The part of the universe that is being studied
Surroundings
Everything outside the system
Energy Profile Diagram
A graph showing the change in energy during the course of a chemical reaction
Reactants
The substances that are present at the start of a chemical reaction
Products
The substances that are formed in a chemical reaction
Activation Energy (Forward)
The energy required for reactants to form the activated complex
Activation Energy (Reverse)
The energy required for products to form the activated complex in the reverse reaction
Effect of Catalyst on Ea
A catalyst lowers the activation energy of a reaction
Effect of Catalyst on ΔH
A catalyst does not change the enthalpy change of a reaction
Effect of Temperature on Rate
An increase in temperature increases the number of particles with sufficient energy and increases the rate of reaction
Effect of Concentration on Rate
An increase in concentration increases the frequency of collisions and increases the rate of reaction
Effect of Surface Area on Rate
An increase in surface area increases the number of collisions and increases the rate of reaction
Effect of Pressure on Rate (gases)
An increase in pressure increases the frequency of collisions between gas particles
Units of Reaction Rate
Concentration per unit time for example mol·dm⁻³·s⁻¹
Measuring Rate by Gas Volume
Measuring the volume of gas produced over time
Measuring Rate by Mass Loss
Measuring the decrease in mass as gas is produced over time
Measuring Rate by Precipitate Formation
Measuring the time taken for a precipitate to form
Dynamic Equilibrium
A state in which the forward and reverse reactions occur at the same rate in a closed system
Closed System
A system in which no matter enters or leaves but energy can be transferred
Open System
A system in which both matter and energy can be transferred
Energy Level of Reactants
The energy possessed by reactants before a reaction occurs
Energy Level of Products
The energy possessed by products after a reaction occurs
ΔH (Calculation)
ΔH is equal to the energy of the products minus the energy of the reactants
Exothermic Energy Profile
A reaction in which reactants have higher energy than products and ΔH is negative
Endothermic Energy Profile
A reaction in which products have higher energy than reactants and ΔH is positive
Catalyst at Molecular Level
A catalyst provides an alternative reaction pathway with a lower activation energy
Reusability of Catalyst
A catalyst is not used up and can be used again
Rate Increase Explanation (General)
The rate of a reaction increases when the number of effective collisions per unit time increases
Arrhenius Theory
A theory stating that only particles with energy greater than or equal to the activation energy can react
Orientation Factor
The requirement that particles must collide in the correct orientation for a reaction to occur
Reaction Mechanism
A series of steps that make up an overall chemical reaction
Intermediate
A substance that is formed in one step and used up in a later step of a reaction mechanism
Rate-Determining Step
The slowest step in a reaction mechanism that determines the overall rate of the reaction
Homogeneous Catalyst
A catalyst that is in the same phase as the reactants
Heterogeneous Catalyst
A catalyst that is in a different phase from the reactants
Enzyme
A biological catalyst that speeds up reactions in living organisms
Inhibitor
A substance that slows down the rate of a chemical reaction
Effect of Temperature on Maxwell-Boltzmann Distribution
An increase in temperature spreads the distribution and increases the number of particles with higher energy
Effect of Catalyst on Maxwell-Boltzmann Distribution
A catalyst does not change the distribution of energies but lowers the activation energy required for reaction
Conservation of Energy in Reactions
Energy cannot be created or destroyed but is transferred during a reaction
Bond Breaking
An endothermic process in which energy is absorbed
Bond Formation
An exothermic process in which energy is released
Limiting Reagent
The reactant that is completely used up in a reaction and determines the amount of product formed
Excess Reagent
A reactant that is not completely used up in a reaction
Initial Rate
The rate of reaction at the beginning of the reaction when concentrations are highest
Average Rate
The change in concentration over a given time interval
Instantaneous Rate
The rate of reaction at a specific point in time
Gradient of Graph
The slope of a graph representing the rate of reaction
Absolute Temperature
Temperature measured in Kelvin
Diffusion
The movement of particles from a region of higher concentration to a region of lower concentration
Adsorption
The process by which reactant particles attach to the surface of a catalyst
Desorption
The process by which product particles leave the surface of a catalyst
Alternative Pathway
A different reaction route with a lower activation energy provided by a catalyst
Energy Barrier
Another term for activation energ