Brainscape's Knowledge GenomeTM

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


See full index

chemistry 😢🥹 > energetics > Flashcards

energetics Flashcards

You may prefer our related Brainscape-certified flashcards:
AP® Chemistry flashcards Periodic Table flashcards Chemistry 101 flashcards Organic Chemistry 101 flashcards
1
Q

what is the definition of an enthalpy change

A

the heat energy it absorbs or releases per mole
it has the symbol ∆h and it always has a sign, a value and units

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

what does a positive sign mean on an enthalpic reaction

A

heat energy - absorbed
- endothermic

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

what does a negative sign mean on an enthalpic reaction

A

heat energy- released
- exothermic

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

what does breaking bonds mean

A

absorbs energy

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

what does making bonds mean

A

releasing energy

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

how can you calculate the enthalpy change for a reaction ?

A

∆h = bonds broken- bonds made

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

what is calorimetry

A

experimental method used to measure enthalpy change

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

when drawing an energy level diagram for an endothermic reaction what do you see ?

A
  • heat energy is absorbed
  • ∆h is positive
  • this means the products end up with more energy than the reactants had
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

when drawing an energy level diagram for an exothermic reaction what do you see ?

A
  • heat energy is released
  • ∆h is negative
  • this means the products end up with less energy than the reactants had
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

what do strong bonds require ?

A
  • more energy to break
  • they also release more energy when made
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

what is a reaction profile diagram

A
  • like an energy level diagram
  • but it shows the path the reaction actually takes from reactants to products
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

what is the energy needed to break the bonds called and what is it represented by in a diagram

A

activation energy and its represented by an arrow from the reactants up to the top of the hump

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

on a reaction profile diagram, what does a hump going from reactants to the products represent

A

new bonds being made

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

what happens with energy in an exothermic reaction

A

energy absorbed < energy released

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

what happens with energy in an endothermic reaction

A

energy absorbed > energy released

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

describe the 3 steps of an exothermic reaction

A

1) the reaction releases heat energy
2) that heat energy is absorbed by the nearby water
3) the temperature of the nearby water increases

17
Q

what are the 2 formulae used to convert your measurements into ∆h

A

1) Q = mc ∆T

2) ∆h = -Q/moles

17
Q

what is combustion calorimetry

A

combusting a fuel to heat up water

18
Q

what is the method to measure the ∆h for the combustion of the liquid fuel methanol

A

1) weigh out 50g of water and place in a can above a burner
2) measure the initial mass of the burner and the initial temperature of the water
3) ignite the burner, stir water for 30 seconds, the extinguish the burner
4) measure the final mass of the burner and the final (maximum) temp of the water

19
Q

how do you calculate your results from a combustion calorimetry reaction?

A
  • first use Q=mc∆T to calculate how much heat energy has been absorbed by the water
    -then use ∆H=-Q/moles, for this we need to convert Q into KJ and calculate the moles of methanol using moles=mass/RFM
20
Q

what are the 2 sources of error in a combustion calorimetry reaction

A
  • heat loss, most of the heat energy dissipates into the air instead of the water
  • incomplete combustion, this releases less heat energy than expected
21
Q

what is solution calorimetry

A

when the reaction you are measuring dissolves in water

22
Q

what is the method for solution calorimetry ( measure the ∆h for the displacement reaction between mg and cuso4)

A

1) pipette 25cm3 of cuso4 into a polystyrene cup, 1cm3 of solution has a mass of 1 g
2) measure the initial temp of the reaction
3) add 1g of mg and stir continuously
4) measure the maximum temp of the solution

23
Q

how to calculate your results from a solution calorimetry reaction

A
  • first use Q=mc∆T to calculate how much heat energy has been absorbed by the water
  • then use ∆h = -Q/moles, for this we need to convert Q into KJ, and calculate the moles of magnesium using moles = mass/RFM
24
Q

what are the sources of error of a solution calorimetry reaction

A
  • heat loss
  • incomplete combustion
  • water being heated means its no longer pure as it has things dissolve in it, that means the specific heat capacity changes
25
Q

can you do calorimetry experiments for endothermic reactions in solution as well ?

A

yes
the reaction absorbs heat energy from the water, so the water cools down
this results in a negative temp change

26
Q

what happens to the minus sign as it gets passed through the equation for a calorimetry experiment for an endothermic reaction and why is it a good thing

A

it comes out the other side as a plus because minus times a minus is a plus
- this is good because reactions that absorb heat energy are endothermic and endothermic reactions are supposed to have positive enthalpy changes

chemistry 😢🥹 (19 decks)

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