1
Q
Why are the signs for the rate of reactants and products different?
A
- since reactants are being consumed, their concentration is decreasing which makes it negative
- since products are being formed, their concentration is increasing which makes it positive
2
Q
What is thermochemistry?
A
study of the energy changes with a physical, chemical and/or nuclear change of a system
3
Q
What is kinetic and potential energy?
A
- Kinetic: energy of motion (anything moving has kinetic energy)
- Potential: stored energy due to the bonds or positon of object
4
Q
What is a system and surroundings?
A
- system: sample being observed
- surroundings: all matter around the system capable of absorbing/releasing thermal energy
- interactions between the two involved exchange of energy/matter
5
Q
What is the 1st law of thermodynamics?
A
total energy of the universe is constant
6
Q
What are chemical systems and the 3 types?
A
- set of reactants and products undergoing transformations
1. Open: can exchange matter/energy with surroundings
2. Closed: can exchange energy but not matter
3. Cannot exchange anything (ideal)
7
Q
What is the difference between heat and temperaure?
A
- Heat: amount of energy transferred between substances, systems, or surroundings
- Temperature: average kinetic energy of the particles in a system
8
Q
What is the 2nd law of thermodynamics?
A
- when two objects are in thermal contact, heat is transferred from object with higher temp to object with lower til they are both the same temp
9
Q
What is Calorimetry?
A
- experimental technique for measuring heat energy changes in chemical system
- calorimeter is used for measuring the heat of the reaction
10
Q
What assumptions are made with calorimetry?
A
- thermal energy exchanged with the calorimeter cups, thermometer, lid can be ignored
- despite substance being dissolved in water, the properties of the water are not affected
- process takes place under constant pressure
11
Q
What is specific heat capacity?
A
The specific heat capacity (c) is the amount of heat energy that is needed to raise the temperature of 1 gram of a substance 1oC (or 1 K).
- depends on type of substance/state of substance
12
Q
What is enthalpy, enthalpy change and molar enthalpy?
A
- The total amount of thermal energy in a substance
- The energy released to or absorbed from the surroundings during a chemical or physical change
- Energy change (absorbed or released) per one mole of a particular reactant or product
13
Q
What assumptions are made with calorimetry when finding molar enthalpy?
A
- No heat transfer between calorimeter & the outside environment
- Any heat absorbed/released by the calorimeter material is negligible
- A dilute aqueous solution is assumed to have the same density and specific heat capacity equal to that of pure water (D = 1.00 g/mL and c = 4.18 J/goC)
- The water of a calorimeter is considered the surroundings and the container in which the process occurs is the system
14
Q
What are the 4 ways enthalpy changes can be represented?
A
- Part of a thermochemical equation
- By writing a chemical equation and stating its enthalpy change
- by stating the molar enthalpy of a specific reaction
- drawing an enthalpy change diagram
15
Q
What does enthalpy change depend on?
A
- For physical and chemical processes, it depends only on reactants and products
- enthalpy change is independent of the process and number of steps to complete
16
Q
What is Hess’s Law?
A
- The value of ∆H for any reaction that can be written in steps equals the sum of the values of ∆H for each individual step in a multistep reaction (ie. it is an additive property)
change of the target equation.
17
Q
What does the slowest step of a reaction tell you?
A
- the rate determining step (overall rate of the reaction depends on the slowest step)
- to speed up a reaction, focus on this step
- takes the longest and has the greatest Ea
18
Q
What is an intermediate and catalyst?
A
- Intermediate: starts as product then used as a reactant
- Catalyst: starts as a reactant then produced as a product
19
Q
what are the 2 requirements for reaction mechanisms?
A
- the equations for the elementary steps must sum to give the overall equation
- the reaction mechanism must agree with the experimentally determined rate law
20
Q
What does “k” in the rate law represent?
A
indicates the speed of a reaction
- small k value = slow reaction
- large k value = fast reaction
21
Q
What is an average and instantaneous rate?
A
- Average Rate – averages the change in [reactants] or [products] per unit of time over a given time interval (secant line)
- Instantaneous Rate is the rate of reaction at a particular point in time (tangent line)
- The rate of the reactant is expressed using a negative sign, whereas the rate of the product is expressed using a positive sign.
22
Q
What are the ways reaction rates can be measured?
A
- collect gas from reaction and measure the volume and pressure changes as reaction occurs (faster reaction = greater change in pressure/volume)
- reactions involving ions have a greater conductivity (more ions formed = greater conductivity)
- reactants changing colour (colour intensity measured by spectrophotometer)
23
Q
What are some factors affecting rate change?
A
Chemical nature of the reactants
Concentration of reactants
Temperature
Presence of a catalyst
Surface area
24
Q
What is collision theory?
A
- For a reaction to occur the reactant particles must collide
- Only a certain fraction of the total collisions cause chemical change; these are called successful collisions
- correct orientation of reactants and sufficient collision energy/activation energy (Ea) needed
25
What is activation energy?
The minimum potential energy increase of a system required for molecules to react
- sufficient Ea needed to break existing bonds and form new bonds
26
What is transition state theory?
- used to explain what happens when molecules collide in a reaction
- It examines the change, from reactants to products
- The kinetic energy of reactants is transferred to potential energy (PE) as the reactants collide, due to the law of conservation of energy
- Transition state can be represented by a potential energy diagram (transition state is at the top of the hill)
27
what is the Maxwell-Boltzmann Distribution?
- The distribution of kinetic energy of entities
28
what are the Theoretical Effect of Chemical Nature of Reactant?
- The rate of any reaction partially depends on the chemical nature of the reactants
- Some molecules have bonds that are relatively weak and have small activation energy barriers which increases reaction rate
- can be colour changing
29
what are the Theoretical Effect of Concentration?
higher concentration of reactant = greater number of particles per unit volume = increase in likelihood of collisions = increased reaction rate
30
what are the Theoretic Effect of Temperature?
increased temperature causes molecules to collide both more often and with more force on average, making an individual collision more likely to be effective = increased reaction rate
31
what are the Theoretical Effect of Catalysts?
- Catalysts accelerate a reaction by providing an alternative lower energy pathway from reactants to products
- If the new pathway has a lower activation energy = a greater fraction of molecules possess the minimum required energy = reaction rate increases
- catalyst do Not increase # of collisions or increase kinetic energy of reactant entites
32
what are the Theoretical Effect of the Surface Area?
- reactants collide only at the surface where the substances are in contact
- Dissolving divides solid or liquid solute into the theoretical maximum number of separate particles, creating the maximum possible surface area. This is why so many reactions occur more quickly in solution
33
What is Standard Molar Enthalpy of Formation?
The quantity of heat energy released/absorbed when one mole of a compound is formed directly from its elements in their standard state (SATP)
34
What are the 2 pros and cons of expanding solar and wind power?
Pros:
- Near-zero operational GHG emissions and local air pollution and creation of jobs for installation and maintenance
Cons:
- Siting and land-use conflicts with wildlife and environmental costs in manufacturing and disposal of panels
and turbines
35
What are the advantages and disadvantages of corn ethanol and how does it work?
- Produced by fermenting starch from maize into ethanol and distilling it for vehicle fuel
Pros:
- Can reduce reliance on petroleum imports and support rural economies.
Cons:
- Lower energy density than gasoline (affects fuel economy), significant water and
fertilizer inputs, and potential food price impacts
36
What are the pros and cons of fuel cells and how do they work?
- electrochemical devices that convert chemical energy directly into electricity
- Pro: produce very low local pollutants
- Con: system costs are expensive
37
What is an alternative equation for mass and moles?
- mass = density x volume
- moles = concentration x volume
12U Chemistry
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