Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Chemistry Y12 > P- Energetics > Flashcards

P- Energetics Flashcards

1
Q

What is net energy change?

A
  • △H
  • diff. in energy between reactants & products
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Energy change during a chemical reaction

A
  • energy is CONSERVED
  • Energy of system + energy of surroundings before reaction = energy of system + surroundings after reaction
  • chemical bonds (mostly covalent) broken + remade –> products
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Why is it important to understand the amount of energy required in a chemical reaction?

A
  1. measure efficiency (energy values of fuels)
  2. calculate energy requirements for an industrial process
  3. calculate theoretical amount of energy needed for bond breaking + making
  4. predict whether or not a reaction will take place
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What does the quantity of heat taken in/ given out in a chemical reaction depends on?

A

Quantity of reactants

– unit: kJ/mol

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

How do you tell from overall energy change whether a reaction is exothermic or endothermic?

A
  • -ve = exothermic
  • +ve = endo
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Why is a reaction exothermic?

A
  • overall temp ↑
  • energy released in making bonds > used to break bonds
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Why is a reaction endothermic?

A
  • overall temp ↓
  • energy to break bonds > released when making bonds
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is enthalpy change?

A

Heat energy change under constant pressure

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is mean bond enthalpy?

A
  • av. amount of energy
  • needed to break a specific type of bond
  • measured over a wide variety of diff. molecules
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Standard conditions

A

∅ - 100kPa
298K

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Explain what is happening in the following reactions.

H2 (g) + 0.5O2 (g) –> H2O (l)

A

Hydrogen GAS reacts with oxygen GAS to form LIQUID water.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Standard enthalpy change of formation (△Hϝ)

A
  • enthalpy change
  • when 1 mole of a substance is formed from its constituent elements
  • in their standard states under standard conditions (298K, 100kPa, 1moldm-3)
  • reactants/ products in standard states
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Standard enthalpy change of reaction (△Hͱ)

A
  • enthalpy change
  • accompanies a reaction in molar quantities shown in chemical equation
  • under standard conditions (298K, 100kPa, 1moldm-3)
  • products & reactnats in standard states

(total energy change- every reaction)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Standard enthalpy change of combustion (△Hϲ)

A
  • enthalpy change
  • when 1 mole of a substance completely reacts w/ O2
  • under standard conditions (298K, 100kPa, 1moldm-3)
  • all reactants & products in their standard states
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is calorimetry?

A

Experiments that measure heat given out by a reaction

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is a simple calorimeter?

A
  • polystyrene cup + thermometer (x lid)
  • only used in solutions
17
Q

Why is bomb calorimeter preferred to simple calorimetry?

A
  • most accurate- measure enthalpy change
  • sealed + insulated –> ↓ chance of heat loss
  • x have to be in solution

:)

  • motorised stirrer- heat distributed uniformly
18
Q

Why is it hard to obtain accurate calorimeter results?

A
  1. some combustion may be incomplete
  2. flammable liquids can be volatile- some may evaporate
  3. some heat lost to surroundings- x transferred to water
19
Q

Explain the difference between heat and temperature.

A
  • Heat: total energy of all particles in given amount of substance
  • Temperature: av. ke of particles in a system (independent on no. of particles)
20
Q

Specific heat capacity def

A
  • amount of heat needed to
  • raise temp of 1g of substance
  • by 1K
  • unit: Jg-1K-1
  • Q=mc△T
21
Q

Law of conservation of energy

A

Energy x created/ destroyed
(only change form/ be distributed in diff. ways)

22
Q

What is Hess’s Law?

A
  • energy change from reactants A to products B
  • is independent of the pathway taken
  • no matter how many stages it involves (intermediate reactions)
23
Q

The enthalpy change of formation of Gold (III) oxide is +81kJ/mol.
What does it say about the stability of the compund?

A
  • unstable
  • ∵ energy is put in to decompose
24
Q

Explain why values from mean bond enthalpy
calculations differ from those determined using
Hess’s law.

A

Mean bond enthalpies (enthalpy for reaction)
- mean values
- across a range of compounds containing that bond

Enthalpies of formation
- ↑ accurate
- ∵ specific to the chemical/ molecule

25
Q

How to find the best estimate of the temperature immediately after mixing?

A
  • draw line of best fit through points
  • extrapolate back to time of mixing
26
Q

Suggest why the value for standard enthalpy of formation of liquid antimony (Group 5 element) given is not zero. (1)

A
  • x in its standard state (should be solid x liquid)
  • △Hϝ of an element in standard state = 0 by def.
27
Q

When is a reaction energetically favourable?

A

when it releases ↑ energy

Chemistry Y12 (33 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions