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Chemistry > Test 2 > Flashcards

Test 2 Flashcards

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1
Q

What energy change occurs in enthalpy

A

Kinetic energy increases with increasing temperature

Potential energy decreases with increasing bond strength

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2
Q

What happens to enthalpy in a reaction

A

During a chemical reaction, bond are broken and new bonds form, so there will be a change in the amount of stored potential energy

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3
Q

What is the enthalpy of a substance

A

The enthalpy of a substance is the total energy present.

Includes potential and kinetic

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4
Q

What is conversion of energy

A

During a chemical reaction the total amount if energy must remain constant.
It may be transformed from one form to another.
If potential energy decreases kinetic energy must increase.
Raises temperature and allows heat to flow out of the system.

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5
Q

What are Exothermic reactions

A

Release heat into the surroundings.

Potential energy in the bonds is lower so potential energy is converted into kinetic and is released from the system

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6
Q

What is endothermic reactions

A

Absorbs heat

Heat energy flows into the system as kinetic energy is converted into potential energy in the bonds of the substances

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7
Q

What is a heat reaction of enthalpy

ALSO KNOWN AS ENTHALPY CHANGE

A

The amount of heat released or absorbed during a chemical reaction

This is known as the enthalpy change of the reaction when it is conducted at constant pressure (lab conditions)

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8
Q

What is the symbol for enthalpy change

A

(Delta) H

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9
Q

How is change in enthalpy measured?

A

Can be determined by measurement of the temperature change that accompanies a chemical reaction

(Delta)H = enthalpy of product- enthalpy of reaction

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10
Q

How can we tell the Enthalpy of an Exothermic reaction is

A

(Delta)H negative
H of product
Heat emitted into the surroundings
Temperature of surroundings increase

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11
Q

How can we tell what the Enthalpy of an endothermic reaction is

A

(Delta)H positive
H of product > H of reactant
Heat absorbed from surroundings
Temperature of surroundings decreases

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12
Q

The (delta)H value of a reaction is shown by

A

H2(g) + Cl2(g) –> 2HCl(g) ; H= -184 kJ

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13
Q

What are thermochemical equations

A

balanced stoichiometric chemical equation that includes the enthalpy change, ΔH.
In variable form, a thermochemical equation would look like this:

A + B → C
ΔH = (±) #
Where {A, B, C} are the usual agents of a chemical equation with coefficients and “(±) #” is a positive or negative numerical value, usually with units of kJ.

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14
Q

What are chemical changes

A

Those in which new substances with different composition and properties are formed

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15
Q

What are physical changes

A

Occurs without altering the chemical composition of a substance

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16
Q

What happens in a chemical reaction

A

A chemical change occurs and new substances are formed.

Reactants: substances that are combined together in the chemical reaction

Products: the new substance formed

Atoms of reactant are rearranged to form product

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17
Q

What happens to bonds in chemical reaction

A

Bonds between atoms are disrupted and new bonds are formed

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18
Q

What are common signs of reaction

A 
Colour change
Formation of a solid 
Production of odour 
Significant change in temperature
Production of gas
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19
Q

What is the Law of conservation of mass

A

Mass is neither created nor destroyed in a chemical a reaction

Mass of the reactant will be the same as the mass of the product

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20
Q

Balanced equations of Chemical equations

A

Because atoms are neither created nor destroyed during a chemical reaction the equation must be balanced

Therefore the number of atoms of each type must be the same on both sides of the arrow

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21
Q

How is the state of a reactant or product indicated

A

(s) - solid
(l) - liquid
(g) - gas
(aq) - in aqueous solution

Ionic equations sometimes written instead of molecular equations for reactions involving ions

Only ions involved in the reaction are shown (others are spectator ions and are not included)

Must be balanced in both atoms and charge

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22
Q

What is a precipitation reaction

A

Occurs when ions in solution combine to form a new compound that is insoluble in water.
Insoluble substance formed is a precipitate

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23
Q

How are precipitates formed

A

When two ionic solutions are mixed together, all the ions remain separate unless one of the combinations can form an insoluble substance

We use ionic equations to represent this because the other ions that remain in solution are not actually involved in the reaction

24
Q

Example of an equation of precipitation

A

AgNO3(ag) + NaCl(aq) —> AgCl(s) + NaNO3(aq)

Is written as

Ag(aq) + Cl(aq) —> AgCl(s)

25
Q

What is Colour prediction

A

The colour of an ionic compound is usually determined by the colour of the ions in which it is composed

Eg. A solid composed of two colourless ions will usually form a white precipitate, a blue ion combined with a colourless ion will usually form a blue precipitate

26
Q

What are exceptions to colour of a precipitate

A

Pb2+ (colourless) and I (colourless)

combine to form PbI2 (yellow)

27
Q

Define relative atomic mass of elements

A

The weighted average of the relative atomic masses of the isotopes compares to 1/12th the mass of an atom of carbon-12

28
Q

Define relative molecular mass

A

Relative molecular mass of a substance is the mass of a molecule of that substance compared to 1/12th the mass of a carbon-12

29
Q

Calculate the relative molecular mass of sucrose, table sugar, which has a molecular formula of
C12H22O11

A

= 12 x Ar(C) + 22 x Ar(H) + 11 x Ar(O)
= (12 x 12.01) + (22 x 1.008) + (11 x 16.00)
= 342.3

30
Q

What is relative formula mass

A

The relative formula mass of a substance is the weighted average of the masses of the formula units relative to 1/12 of the mass of a carbon-12 atom.

31
Q

What is a mole

A

One mole is the amount of substance containing Avogadro’s number of particles. This number is:
6.02 x 10^23

32
Q

What is molar mass

A

The mass of one mole of a substance is called its molar mass (M)
This mass is simply, the relative atomic mass (Ar) or relative formula mass (Mr), expressed in grams per mole.

33
Q

Example of molar mass (Na)

A

So, molar mass of M(Na) = mass of 1 mol of Na atom

We know that Ar(Na) = 23.0
Therefore M(Na) = 23.0 g mol -1
34
Q

Example of molar mass = M(SO2)

A

Ar(S) + 2 x Ar(O)

  1. 07 + 2 x 16.00
  2. 07 g mol-1
35
Q

Calculations - mass to moles

A

The number of moles of a substance in a given mass can be calculated by

n = m/M

Where:
n is number of moles
m is mass of the substance
M is the molar mass of the substance

36
Q

Example of mass to mole- calculate the number of moles of sodium chloride in 200g

A

M(NaCl) = 22.99 + 35.45
= 58.44 g mol-1

n(NaCl) = m/M
= 200/58.44
= 3.42 mol

37
Q

How is Mole to mass equation written

A

m = M x n

38
Q

What are Chemical formulas and moles

A

The formula of any given substance indicates the number of atoms present in a molecule of a substance

The same concept can be applied to the moles of a substance.

39
Q

What does 1 mole of H2CO3 cobtains

A

2 mol of H atoms
1 mol of C atoms
3 mol of O atoms

40
Q

What is Percentage composition

A

Percentage composition is the percentage of a formula mass represented by each element.
Percentage composition compares the mass of one part of a substance to the mass of the whole.

41
Q

How do you find percentage composition

A

-

42
Q

Determine the percentage composition by mass for each element in silver nitrate

A 
Mr(AgNO3) = 107.9 + 14.01 + 3 (16.00) = 169.91
%(Ag) = 107.9/169.91 x 100 = 63.50%
%(N) = 14.01/169.91 x 100 = 8.24%
%(O) = 48/169.91 x 100 = 28.25%
43
Q

How do you write a balanced equation

A

1) write word equation
2) unbalance equation showing correct formulae
3) balance the equation

44
Q

Examples of exothermic reactions

A

Petrol burns, energy is released

45
Q

Examples of endothermic reaction

A

Melting ice, id you place the ice cube in the glass of water, it cools it down

46
Q

Gaseous molecules can have kinetic energy due to the three different types of motion.
What are these three types

A

Vibrational
Rotational
Translational

47
Q

Define Vibrational motion

A

Atoms move away and towards each other

48
Q

Define rotational motion

A

Molecules rotates about its centre

49
Q

Define transitional motion

A

Molecules moves from place to place

NOT ALL ATOMS HAVE TRANSITIONAL MOTION

50
Q

How do you write a balanced equation

A

1) write word equation
2) unbalance equation showing correct formulae
3) balance the equation

51
Q

Examples of exothermic reactions

A

Petrol burns, energy is released

52
Q

Examples of endothermic reaction

A

Melting ice, id you place the ice cube in the glass of water, it cools it down

53
Q

Gaseous molecules can have kinetic energy due to the three different types of motion.
What are these three types

A

Vibrational
Rotational
Translational

54
Q

Define Vibrational motion

A

Atoms move away and towards each other

55
Q

Define rotational motion

A

Molecules rotates about its centre

56
Q

Define transitional motion

A

Molecules moves from place to place

NOT ALL ATOMS HAVE TRANSITIONAL MOTION

Chemistry (4 decks)

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