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Chemistry > Quantitive chemistry and chemical changes > Flashcards

Quantitive chemistry and chemical changes Flashcards

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1
Q

how do you calculate the percentage mass of an element in a compound

A

atomic mass x number of atoms of the element / relative formula mass of the compound

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2
Q

how do you calculate the number of moles

A

mass in g / relative formula mass

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3
Q

in an exothermic reaction is heat given in or out

A

given out

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4
Q

in an endothermic reaction is heat given in or out

A

taken in

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5
Q

does an exothermic reaction transfer energy to or away from the surroundings

A

transfers energy to the surroundings usually by heating

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6
Q

does an endothermic reaction take energy form the surroundings or transfer energy to the surroundings

A

the reaction takes energy from the surrounding

this is shown by a fall in temperature

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7
Q

give an example of an exothermic reaction

A

hand warmers

self heating cans

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8
Q

give an example of an endothermic reaction

A

sports injury packs

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9
Q

explain a exothermic reaction

A

this reaction is exothermic because energy needed to break the bonds is less than energy released in bond formation

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10
Q

explain a endothermic reaction

A

energy released in bond formation
is less than
energy needed to break the bonds

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11
Q

are endothermic reaction energy changes positive or negative

A

positive +

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12
Q

are exothermic reaction energy changes positive or negative

A

negative -

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13
Q

explain bond energies

A

when we want to break a chemical bond, it requires energy normally endothermic

this then releases energy normally exothermic

every chemical bond has an energy value

this tells us the energy needed to break the bond

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14
Q

is breaking bonds endo or exo themic

A

endothermic +

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15
Q

why is it not always possible for a 100% yield

A

product is lost in transfer

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16
Q

give the equation of percentage yield

A

product that was actually produced / product that should of been produced x 100

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17
Q

why can we not achieve more than 100% yield

A

because it means you would have created atoms and that is not possible

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18
Q

state what is meant by an exothermic reaction

A

an reaction that releases energy

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19
Q

in energy transfer diagrams, exothermic,

do the products have more or less energy than the reactants

A

less

because energy is being transferred from the reaction to the surroundings

20
Q

in energy transfer diagrams, endothermic

do the products have more or less energy than the reactants

A

more

because energy has been taken in from the surroundings

21
Q

if the products have more energy than the reactants what does this mean

A

energy has been taken in from the surroundings

energy increases

endothermic
positive

22
Q

if the products have less energy than the reactants what does this mean

A

energy is being transferred from the reaction to the surroundings,

energy decreases

  • exothermic
    negative
23
Q

if a reversible reaction is exothermic in one direction what happens to the other direction

A

it is endothermic in the opposite direction

the same amount of energy is transferred in each case

24
Q

what is a dynamic equilibrum

A

rate of forward reaction is equal to rate of backward reaction in a closed system

25
Q

what happens if temperature is increased in an reversible reaction

A

if temperature increases, endothermic reaction is favoured

26
Q

what happens if temperature is increased in an exothermic reaction

A

if temperature increases, exothermic reaction is favoured

27
Q

what is the effect of pressure

A

pressure favours the reaction which produces fewer molecules

meaning the reaction will produce more of the favoured reactions

28
Q

what happens in a dynamic equilibrium

A

concentration of reactants and products stay constant

29
Q

what must happen in a dynamic equilibrium

A

reaction must be reversible

reaction must undergo in a closed system so no change of matter, but energy can still be exchanged

30
Q

what is the calculation of concentration.

A

mass (g) / volume (dm3)

31
Q

if we increase the mass of solute and keep the volume the same what happens to the concentration

A

it stays the same

32
Q

if we increase the volume of solution and keep the mass of solute the same what will happen to the concentration

A

it will decrease

33
Q

what is atom economy

A

is the measure of the amount of starting materials that end up as useful products

34
Q

what is the equation of atom economy

A

mr of desired products / mr of all reactants (from equation) x 100

35
Q

what is the equations for atomic mass

A

(Ar x Adundance) + (Ar x abundance) // 100

36
Q

what is the equation for moles in solids

A

mass / Mr

37
Q

what is the equation for moles in gases

A

if in dm3

volume dm3 / 24dm3

if in cm3

volume cm3 / 24000

38
Q

what is the equation for concentration?

A

mols or mass / volume dm3

39
Q

what is a reversible reaction

A

when the products can react together to make the reactants

40
Q

what is a closed system

A

when no exchange of matter can occur only energy can be transferred

41
Q

effect of increasing temperature in a dynamic equilibrium

A

a increase of temperature favours endothermic reaction

42
Q

effect of increasing pressure in a dynamic equilibrium

A

an increase in pressure favours the side with the least moles (molecules)

43
Q

effect of concentration in a dynamic equilibrium

A

an increase in concentration of reactants

move the equilibrium forwards direction

to make more products

44
Q

explain in terms of bond making and breaking why a reaction is endothermic

A

energy released in bond formation
is less than
energy needed to break the bonds

45
Q

explain in terms of bond making and breaking why a reaction is exothermic

A

energy released in bond formation
is more than
energy needed to break the bonds

46
Q

explain why a non metal has a low boiling point

A

simple molecular structure
weak intermolecular forces
little energy needed to overcome these

Chemistry (7 decks)

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