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✅Chemistry Unit 2 > đŸ”´đŸ”¸2.1 -thermochemistry > Flashcards

đŸ”´đŸ”¸2.1 -thermochemistry Flashcards

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1
Q

Define an exothermic reaction

A

A reaction that releases energy to the surroundings, there is a temperature rise and đŸ”¼H is negative

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2
Q

Define an endothermic reaction

A

A reaction that takes in energy from the surroundings, there is a decrease in temperature and đŸ”¼H is positive

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3
Q

What is the kinetic energy of matter?

A

The energy of motion at a molecular level

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4
Q

What is the cause potential energy of matter?

A

The positions of atoms relative to one another

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5
Q

What requires a change in potential energy?

A

Bond-breaking and bond-making

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6
Q

What is the internal energy of a system?

A

The sum of the kinetic energy of all of the particles in a system and their potential energy

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7
Q

Give 3 examples of exothermic reactions

A
  • reacting acids with metals
  • thermite reaction
  • combustion
  • respiration
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8
Q

Give 3 examples of endothermic reactions

A
  • melting ice
  • photosynthesis
  • thermal decomposition of group 2 carbonates
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9
Q

Define enthalpy (H)

A

The heat content of a system at constant pressure

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10
Q

Define enthalpy change (đŸ”¼H)

A

The heat added to a system at a constant pressure

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11
Q

What is the standard pressure?

A

101KPA

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12
Q

Name an equation to calculate enthalpy change

A

Enthalpy of products - enthalpy of reactants

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13
Q

Which line is higher in an exothermic enthalpy profile, The products or reactants.

A

The reactants line is higher than the products therefore (đŸ”¼H) is negative

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14
Q

Which line is higher in an endothermic enthalpy profile, The products or reactants.

A

The products line is higher than the reactants therefore (đŸ”¼H) is positive

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15
Q

Give an example of an exothermic reaction

A

H2 (g) + 1/2O2 (g) —> H20 (g)

đŸ”¼H = -242

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16
Q

Define the principle of the conservation of energy

A

States that energy can’t be created or destroyed only changed from one form to another

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17
Q

Name the standard conditions

A
  • all substances in standard states
  • temperature of 298K (25 degrees)
  • A pressure of 1 atm (101,000 Pa)
18
Q

What Is enthalpy change of formation?

A

Enthalpy change when one mole of a substance is formed from its constituent elements

19
Q

What is the standard enthalpy change of formation of carbon dioxide?

A

C(s) + O2 (g) —> CO2 (g)

20
Q

What is the standard enthalpy of formation of carbon monoxide

A

C(s) + 1/2O2 (g) —-> CO (g)

21
Q

Name the essential point to consider when looking at enthalpy change equations

A

That enthalpy change occurs at 1 mole therefore the molecule in the substance must remain at 1 mole and the other molecules must be balanced around this.

22
Q

What is the enthalpy change of all elements in their standard state?
Why?

A

0 KJmol -1

Because there is no chemical change occurring

23
Q

What is the standard enthalpy change of combustion

A

The enthalpy change when one mole of a substance is completely combusted in oxygen

24
Q

What is the standard enthalpy change of combustion of Hydrogen

A

H2 (g) + 1/2 O2 (g) —> H2O (l)

25
Q

What is the standard enthalpy change of combustion of methane

A

CH4 (g) + 2O2 (g) —> CO2 (g) + 2H2O (l)

26
Q

What is the enthalpy change of reaction

A

Enthalpy change In a reaction between the number of moles of reactants shown in the equation for the reaction
E.g double the moles = double the enthalpy

27
Q

How do you calculate the enthalpy change of formation?

A

Enthalpy change of reaction = sum of the enthalpy change of formation of the reactants - the sum of the enthalpy change of formation of the products

28
Q

What is Hess’s law?

A

Hess’s law states that the total enthalpy change for a reaction is Independent of the route taken from the reactants to the products

29
Q

How do you demonstrate Hess’ law?

A

Enthalpy change cycle diagrams

30
Q

What do you break the bottom of the enthalpy cycle into during a enthalpy change of formation

A

Carbon dioxide + water

NEED TO PRACTICE QUESTIONS

31
Q

What do you break the bottom of the enthalpy cycle into during a enthalpy change of reaction

A

Into its elements

NEED TO PRACTISE QUESTIONS

32
Q

Define bond enthalpy

A

The enthalpy required to break a covalent X-Y bond into X atoms all in the gas phase

33
Q

Why is the value of bond enthalpies always positive

A

Because breaking a bond requires energy

34
Q

Define average bond enthalpy

A

The average value of the enthalpy requires to break a given type of covalent bond in the molecules of a gaseous species

35
Q

Why is the average bond enthalpy calculated

A

Because bond enthalpy can vary depending on the structure of the rest molecule, e.g. C-C in ethane (C2H6) has a different value to C-C in pentane (C5H12)

36
Q

What is the specific heat capacity?

A

Energy requires to raise the temperature of 1g if a substance by 1k

37
Q

What is the specific heat capacity of water?

A

4.18 jg-1K-1

38
Q

What letter is the amount of heat transferred represented by?

A

q

39
Q

Name the equation showing the relationship between temperature change and amount of heat transferred

A

q=mcđŸ”¼T

Amount of heat transferred = mass of solution x specific heat capacity x difference in temperature

40
Q

Name the equation to show the enthalpy change of a reaction per mole

A

đŸ”¼H = -q/n
Enthalpy change = - value of heat transferred/ moles reacted
(NEED TO DO EXAMPLE QUESTIONS)

41
Q

What do we always assume the density of a solution is?

A

1.00gcm-3 (same as water)

42
Q

What are the 3 steps to calculate the molar enthalpy change in displacement, neutralisation, dissolving a solid to form an aqueous solution and combustion reactions ?

A

Step 1: calculate the value of heat transferred in experiment using q=mcđŸ”¼T

Step 2: calculate the amount in moles of the reactants using n = m/Mr

Step 3: Calculate the molar enthalpy change using đŸ”¼H = -q/n

✅Chemistry Unit 2 (8 decks)

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