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54 Cards in this Set
- Front
- Back
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What are the three basic changes? |
Physical, chemical and nuclear. |
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What's a physical change? |
It's a change of state. Intermolecular forces are here. Low energy. |
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What's a chemical change? |
Change to structure/type of particle in molecule. Bonds (covalent/ionic). Moderate energy. |
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What's a nuclear change? |
Change with atom -> neutrons. HIGH energy. |
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What's thermochemistry? |
The amount of heat transferred between a chemical system and its surroundings during a chemical reaction. |
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What's thermal energy? |
It's the kinetic energy (movement) of particles. |
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What's heat? |
Q. Amount of energy transferred between substances. |
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What's temperature? |
A measure of the average kinetic energy (Ek) of particles in a substances. |
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What's a chemical system? |
It's a set of reactants and products under study, and it's represented by a chemical equation. |
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What are the surroundings? |
All the matter around the system that's capable of absorbing or releasing thermal energy. |
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What's endothermic? |
Absorbs thermal energy as heat flows into the system (energy going in). |
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What's exothermic? |
Releases thermal energy as heat flows OUT of the system (energy leaving). |
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What's an open system? |
BOTH matter and energy move FREELY, in and out. |
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What's a closed system? |
MATTER is trapped. Energy moves freely. |
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What's an isolated system? |
BOTH MATTER AND ENERGY ARE TRAPPED. |
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What's calorimetry? |
Process to measure energy changes in a chemical system. Like what we did in bio. |
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What's specific heat capacity? |
The amount of energy needed to raise 1g of substance by 1 degree celsius. |
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What's the specific heat capacity for water? |
4.184 J/gxC |
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What's the equation for calorimetry problems? |
q=mc(delta)t also qrxn=-q of the surroundings Q is negative for the one losing energy/lowering temp. |
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What's an enthalpy change (delta H). |
The difference in enthalpies of reactants and products during a change. Energy surroundings = Equal and opposite of the Enthalpy system. |
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What's an enthalpy? |
The energy associated with the physical/chemical change of a substance. |
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What's molar enthalpy? |
It's the energy change associated with a physical, chemical or nuclear change involving 1 mol of a substance. |
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What's the equation for molar enthalpy? |
delta H=n(delta)Hx (delta)Hx - refers to a specific physical and chemical change Hcomb: combustion. Hvap: gas. Hfusion - melting freezing. Hneut - neutralization. First H: enthalpy (kJ), Hx: molar enthalpy of specific process n: molar # EXOTHERMIC: -Hx (giving energy). Endothermic : + Hx (accepting energy) |
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What's the law of conservation of energy? |
The total energy change of the chemical system is equal to the total energy change of the surroundings. H system = +/- |q surroundings|. |
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What's Hfusion? |
Between solid and liquid (melting and feezing). |
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What's Hvaporization: |
Between liquid and gas (boiling/condensing). |
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What are the types of enthalpy changes? |
Physical: energy is used to overcome the intermolecular forces to force them to act. -fundamental particles remain unchanged. -temperature remains during changes of state -temperature changes during dissolving of pure substances CHEMICAL: -energy changes overcome the electronic structure and chemical bonds in the particles (atoms/ions). -new substances with new chemical bondings are formed. NUCLEAR: -energy changes overcome the forces between protons and neutrons in nuclei. -new atoms w/ different # of protons/neutrons are formed. |
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4 Ways of representing enthalpy changes? |
Thermochemical equations with energy terms. Exothermic, on the right side. Term + term -> term + 33434934 kj or smth. Endothermic, on the left side. Term +33434934 kj or smth -> term + term Thermochemical equations with H values: Exothermic: negative. Endothermic: positive. Molar enthalpies: ex. Hcombustion= -882.0 kj/mol CH4 -be specific with subscript. -state type of rxn w/ molecule. -the unit is kj/mol bc reaction requires heat. Potential Energy Diagram. |
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What's Hess's Law? |
The value of the H for any rxn can be written in steps equal the sum of the values for each individual steps. H= H1 + H2 + H3... |
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What are standard enthalpies of formation? |
-the quantity of energy associated with the formation of one mole of a substance from its elements in their standard states. -3rd way of calculating enthalpy change. |
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What's standard state? |
How the element is found in nature. |
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How do you write formation equation? |
Step 1: write 1 mole of product in the state specified. -write the reactant elements in their standard states. -choose equation coefficients for the reactants to give a balanced equation yielding one mole of product. Endothermic/Exothermic is concerned with the overall net reaction and the bonds in reactants/products. -Determining enthalpies of ions. H={nHpdts + nH rcts} |
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What are chemical kinetics? |
The study of ways to make chemical reactions go faster or slower. |
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Whats a rate of reaction? |
The speed at which a chemical change occurs. -expressed as a change in concentration per unit time. Rate (mol/LxS) = delta Concentration (mol/L) / delta time (s) |
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What's average rate of reaction? |
The speed at which a reaction proceeds over a period of time. measuered as a change in concentration of a reactant or product over time. |
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What's instantaneous rate of reaction? |
the speed at which a reaction is proceeding at a particular point in time. |
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What are the three ways of measuring reaction rates? |
Reaction that produces gas: faster reaction, greater change in volume/pressure. Reaction that involves ions: reaction proceeds and more ions form, the conductivity of solutions increases. Reaction that change colour: use a spectrophotometer to measure color intensity or the wavelengths of light that are visible to humans. |
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What are the factors affecting reaction rate? |
You need: correct chemical. energy. good concentration of particles. |
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What are the 5 factors affecting rate? |
Chemical nature of reactants. Concentration of reactants. Temperature. Presence of catalyst. Surface Area. |
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Chemical Nature of Reactants. |
In homogeneous chemical systems: -reactions of monatomic ions (Ag , Cl), extremely fast rate . -Reactions of molecular substances (C6H12O6) - much slower rate. Strenght and location of bond(s) in a particular structure affect the effectiveness of a collision. -Molecules aren't moving at the same speed, most are in a mid-range of kinetic energy. Maxwell-Boltzmann distribution. Threshold energy: the minimum kinetic energy required to convert Ek to Ea during the formation of the activated complex. |
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Concentration of reactants. |
Higher concentration of reactants, greater # of particles per unit volume, higher chance of them colliding, higher rxn rate. |
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Temperature. |
High temp : molecules collide often w more force so increased ROR. Low temp: the opposite. decreases ROR. |
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Presence of catalyst: |
Catalyst: a substance that alters the rate of a chemical reaction without itself being permanently changed. -a catalyst increases the rate of rxn because a larger fraction of collisions is effective. Heterogenous catalyst: reactants and catalysts are in different physical states. Homogeneous: they're in the same physical states. |
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Surface Area. |
Higher surface area = more space to collide with = higher rxn rate. Rxn w finely divided iron has more surface area than a solid piece, so ROR is faster. |
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What's activation energy? |
it's the minimum increase in potential energy of a system that's required for the molecules to react. |
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What's an activated complex? |
If the molecules have enough kinetic energy, they'll approach closely enough so that their bond structures rearrange to form an activated complex. It's unstable chemical species that has partially broken and partially formed bonds representing the maximum potential energy point in the change. The mac potential energy change, so the transition state. |
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What's the rate law equation? |
The relationship among rate, the rate constant, the initial concentrations of reactants and the orders of reaction with respect to the reactants. |
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What's half life? |
The time required for one half of the sample to react. |
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What's a reaction mechanism |
It's a sequence of elementary steps which total to the overall reaction. |
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What are the 3 main concepts of collision theory? |
Particles are always moving around and smashing into each other. An effect collision breaks bonds or forms new ones. An ineffective collision, colliding particles rebound and are unchanged. Rate = frequency of collisions x fraction of effective collisions. |
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Elementary step: |
A step in a reaction mechanism that only involves 1-2-3- particle collisions. |
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Rate Determining Step (RDS) |
The slowest step in a reaction mechanism. |
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Reaction intermediates. |
Molecules formed as short-lived products in reaction mechanism. -1st product then reactant. catalyst : reverse, |
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How do you find RDS? |
Find the step with the most molecules. That's the slowest because they take longer to react. Also, you can find the step with the most stable reactants, they're more stable and harder to change/react. |
