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Higher chemistry > Unit 3 > Flashcards

Unit 3 Flashcards

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1
Q

What is the collision theory?

A

for a chemical reaction to take place the reactant particles must collide

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2
Q

What things is needed for collisions to be successful?

A

Correct geometry, enough energy to overcome the activation energy

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3
Q

What is activation energy?

A

the energy required for a reaction to take place

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4
Q

what is the definition of the activated complex?

A

an unstable arrangement of atoms

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5
Q

Where is the activated complex on an energy diagram?

A

very top of the curve

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6
Q

How can we increase the speed of reactions, what happens to the particles?

A

increase temp- gives particles energy, more successful collisions.
increase concentration- more particles, more successful collisions

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7
Q

What does a catalyst do in a reaction?

A
  • speeds up reaction by providing alternative route and lowering activation energy
    =>if less energy is required for successful collisions then more collisions are likely to happen
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8
Q

What happens to the activation energy if we increase the temperature?

A

nothing

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9
Q

What is a homogeneous catalyst?

A

a catalyst that’s in the same physical state as the reactants

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10
Q

What is a heterogeneous catalyst?

A

a catalyst that’s in a different physical state from the reactants

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11
Q

What are the names of the three stages of how heterogeneous catalyst’s work?

A
  1. Adsorption
  2. reaction
  3. desorption
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12
Q

Give a summary of each stage of how heterogeneous catalysts work?

A
  1. Adsorption- absorbing reacting molecules on active site & holds with weak bonds. causes bonds within molecule to weaken.
  2. reaction- reaction occurs with less activation energy to form activated complex
  3. desorption- product molecules are formed and leaves catalyst’s surface
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13
Q

What is catalyst poisoning?

A

when another substance attaches to active site. irreversible

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14
Q

What is an exothermic reaction?

A

a reaction that releases heat (-ve)

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15
Q

What is an endothermic reaction?

A

a reaction that takes in heat (+ve)

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16
Q

What is enthalpy change?

A

energy difference between products and reactants

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17
Q

How can we tell on an energy diagram if the reaction is exothermic or endothermic?

A

EXOTHERMIC- products lower than reactants
ENDOTHERMIC- products higher than reactants

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18
Q

Definition of enthalpy of combustion

A

energy released when 1 mole of a substance is completely burned in oxygen

19
Q

What are the products of complete combustion?

A

water and carbon dioxide

20
Q

What are the sources of error for experimental vs theoretical values?

A
  • not enough oxygen for complete combustion
  • some fuel evaporates
  • no lid on container
  • if water has not been stirred
  • some heat energy absorbed by beaker
21
Q

How can a bomb calorimeter be used to improve the experiment?

A
  • heat no longer lost to surroundings
  • complete combustion occurs
22
Q

What is molar bond enthalpy?

A

energy required to break one mole of chemical bonds in the gaseous state and form two moles of gaseous atoms

23
Q

What id mean bond enthalpies?

A

bonds that are found in more than one substance

24
Q

What are the steps of finding enthalpy change

A
  1. draw full structural formula to show all bonds
  2. write a list of all bonds broken (+) in reactants
  3. write a list of bonds made (-) in products
  4. write in bond enthalpy values for each
  5. calculate total energies
  6. calculate enthalpy change using equation
25
Q

What is Hess’s law?

A

Hess’s ;aw states that the enthalpy change for a chemical reaction is independent of the route taken

26
Q

What is a closed system?

A

where reactants and products are not aloud to escape

27
Q

What happens in a reaction when it reaches equilibrium?

A

at equilibrium the reactants change into products at exactly the same rate at which the products change into reactants. this only occurs in a closed system. The reaction has NOT stopped

28
Q

what is dynamic equilibrium?

A

in a closed system, when the rate of the foward and reverse reactions are equal, and the concentrations of products and reactants are constant

29
Q

How do chemists maxamise product?

A

chemists employ strategies to change the position of the equilibrium in favor of the products

30
Q

What is le chatelier’s principle?

A

if a system at equilibrium is subjected to any change the system readjusts itself to counteract the applied change

31
Q

What do we say if the forward reaction is favored?

A

the equilibrium has shifted to the right

32
Q

What do we say if the reverse reaction is favored?

A

the equilibrium has shifted to the left

33
Q

What things can be changed to shift the position of equilibrium?

A
  • concentration
  • temperature
  • pressure
34
Q

What happens to the position of equilibrium if we increase the concentration on the products and reactants?

A

INCREASE REACTANTS- favor forward reaction & products
INCREASE PRODUCTS- favor reverse reaction & reactants

35
Q

What happens to the position of equilibrium if we decrease the concentration on the products and reactants?

A

DECREASE REACTANTS- favor reverse reaction & reactants
DECREASE PRODUCTS- favor forward reaction & products

36
Q

What happens to the position of equilibrium if we increase and decrease the temperature?

A

INCREASE- favors endothermic reaction (+ve)
DECREASE- favors exothermic reaction (-ve)

37
Q

What happens to the position of the equilibrium if we increase and decrease pressure?

A

INCREASE- favors side with least GASEOUS moles
DECREASE- favors side with most GASEOUS moles

38
Q

What happens to the position of equilibrium if we add a catalyst?

A

NOTHING- a catalyst speeds up the forward and reverse reaction at the same rate, no overall change.
IF A QUESTION ASKS WHAT HAPPENS TO THE FORWARD/REVERSE REACTION IT INCREASES

39
Q

When will pressure not change the position of the equilibrium?

A

when there’s an equal number of gaseous moles on each side

40
Q

What is a standard solution?

A

a solution of an accurately known concentration

41
Q

How can an endpoint of a titration be shown?

A

by using an indicator

42
Q

How do we accurately measure solutions in a titration?

A

by using a pipette

43
Q

Why are titration’s used?

A

to determine unknown concentration

Higher chemistry (3 decks)

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