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Chemistry IGCSE > Energetics > Flashcards

Energetics Flashcards

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1
Q

What can happen to energy during a chemical reaction (process)?

A

energy can either be absorbed or released from / to the surroundings

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1
Q

Define exothermic

A

energy released (temp. increases)

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2
Q

Define endothermic

A

energy absorbed (temp. decreases)

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3
Q

Can energy change in a reaction be measured? If so, how? If not, why?

A

yes it can, it is measured as enthalpy change

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4
Q

Define enthalpy

A

energy stored in chemicals that can be released as heat (stored in bonds)

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5
Q

What is the symbol and unit for enthalpy change?

A

symbol - △H
unit - kJ / mol

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6
Q

Define Ea (activation energy)

A

minimum energy required for particles to react

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7
Q

When a reaction is exothermic,
energy in reactants < or > energy in products

A

>

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8
Q

What is shown by the blue arrow?

What is shown by the blue arrow?
A

Ea, activation energy

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9
Q

What should be on the x-axis of an energy profile and what should be on the y-axis?

A

x-axis = time / progress of reaction

y-axis = energy

Check page on energetics (9th grade)

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10
Q

When a reaction is endothermic,
energy in reactants < or > energy in products

A

<

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11
Q

What is the equation of energy in a reaction

A

q = mc△T

energy in reaction (J)
= mass of chemical being heated * (specific heat capacity - water =4.18 J/ºc/g) * temperature change (ºc/K)

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12
Q

What is this apparatus called?

A

calorimeter

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13
Q

Why is the coffee cup in a beaker when measuring the enthalpy change in a solution of KNO₃ and NH₄Cl? Why should you keep stirring the mixture?

A

to stop it from falling over

keep stirring to spread energy evenly

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14
Q

When measuring the enthalpy change in a solution of KNO₃ and NH₄Cl, what do you need to measure?

A

mass, initial and final temperature, volume of water

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15
Q

Define bond enthalpy

A

quantity of energy needed to break one mole of a specific type of bond

16
Q

Is the process of breaking electrostatic forces between atoms exothermic or endothermic?

A

endothermic

17
Q

Is forming bonds exothermic or endothermic?

A

exothermic

18
Q

Which bonds are affected by temperature and which are not?

A

IMFs are affected by temperature and covalent bonds are not

19
Q

Only covalent bonds are not affected by temperature. What can be assumed by this statement?

A

that, therefore, bond enthalpies only apply to covalent substances

20
Q

Complete the sentence with endothermic or exothermic:
_________________ reactions have stronger / more bonds in the products (compared to reactants)

A

exothermic

21
Q

Complete the sentence with endothermic or exothermic:
_________________ reactions have weaker / less bonds in the products (compared to reactants)

A

endothermic

22
Q

How do you calculate △H using bond enthalpies? How do you know if the reaction in exothermic or endothermic?

A

Add up all of the bond enthalpies in the reactants. Do the same for the products. Calculate the bond enthalpy change by subtracting the bond enthalpies of the reactants from the bond enthalpies of the products. If the answer is negative, it’s exothermic, and vice versa.

23
Q

How is bond enthalpy calculated?

A

△H = sum of bonds broken − sum of bonds made

24
Q

What is the symbol for enthalpy change of combustion?

A

△H꜀

25
Q

When measuring enthalpy change for combustion, you have the measure the mass of…

A

just the water (chemical being heated)

26
Q

When measuring enthalpy change in combustion, what is the role of an insulator? What is the insulator that is usually used?

A

insulator usually used = polystyrene (plastic)
insulator avoids energy gain / loss

27
Q

What is the symbol for enthalpy change of neutralisation?

A

△Hₙ

28
Q

Define △Hₙ

A

enthalpy change when 1 mole of water forms from acid + base

29
Q

When doing a reaction of enthalpy change of neutralisation, which apparatus is used to measure the acid?

A

pipette

30
Q

When doing a reaction of enthalpy change of neutralisation, which apparatus is used to measure the base?

A

burette

31
Q

acid + metal carbonate →

A

salt + water + carbon dioxide

32
Q

Describe what is happening in letter A

A

temperature increases as acid and base react

33
Q

Describe what is happening in letter B

A

temperature decreases as colder liquid is added

34
Q

Fill in the blanks (blacks)

A

Pink arrow - max temperature
Grey arrow - volume required

Chemistry IGCSE (13 decks)

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