Thermochemistry
This presentation is the property of its rightful owner.
Sponsored Links
1 / 21

Thermochemistry PowerPoint PPT Presentation


  • 62 Views
  • Uploaded on
  • Presentation posted in: General

Thermochemistry . DO NOW. The specific heat of ethanol is 2.44 J/ g°C . How many kilojoules of energy are required to heat 50.0 g of ethanol from -20.0°C to 68°C?. Objective . Describe how calorimeters are used to measure heat flow . Construct thermochemical equations .

Download Presentation

Thermochemistry

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Thermochemistry

Thermochemistry


Do now

DO NOW

  • The specific heat of ethanol is 2.44 J/g°C. How many kilojoules of energy are required to heat 50.0 g of ethanol from -20.0°C to 68°C?


Objective

Objective

  • Describe how calorimeters are used to measure heat flow.

  • Constructthermochemical equations.

  • Solve for enthalpy changes in chemical reactions by using heats of reaction.


Calorimetry

Calorimetry

  • Calorimetry - the measurement of the heat into or out of a system for chemical and physical processes.

    • Based on the fact that the heat released = the heat absorbed

  • The device used to measure the absorption or release of heat in chemical or physical processes is called a “Calorimeter”


Enthalpy

Enthalpy

  • Heat absorbed or released by a reaction at constant pressure

    H = qq = H = m x C x T

    Note: We cannot calculate the actual value of enthalpy, only the change in enthalpy


Thermochemical equation

Thermochemical equation

  • Includes the ΔH as either a product or a reactant

    CaO(s) + H2O(l)  Ca(OH)2(s) + 65.2 kJ


Heat of reaction

Heat of Reaction

H = Hproducts – Hreactants


Exothermic reaction

Exothermic Reaction

2CO(g) + O2(g)  2CO2(g) H = -566.8 kJ

Or

2CO(g) + O2(g)  2CO2(g) + 566.8 kJ

Negative sign means energy is released


Thermochemistry

Energy

Change is down

ΔH is <0

= Exothermic (heat is given off)

Reactants

®

Products


2co g o 2 g 2co 2 g 566 8 kj

2CO + O2

Energy

2CO2

Reactants

®

Products

2CO(g) + O2(g) → 2CO2(g) + 566.8 kJ

566.8kJ given off


Endothermic reaction

Endothermic Reaction

2CO2(g)  2CO(g) + O2(g) H = +566.8 kJ

Or

2CO2(g) + 566.8 kJ  2CO(g) + O2(g)

Positive sign means energy is absorbed


Thermochemistry

Energy

Change is up

ΔH is > 0

= Endothermic (heat is absorbed)

Reactants

®

Products


Thermochemistry

2CO(g) + O2(g)

Energy

2CO2(g)

Reactants

®

Products

CaCO3→ CaO + CO2

2CO2(g) + 566.8 kJ →2CO(g) + O2(g)

566.8kJ absorbed


Chemistry happens in

Chemistry Happens in

MOLES

  • An equation that includes energy is called a thermochemical equation

  • CH4 + 2O2® CO2 + 2H2O + 802.2 kJ

    • 1 mole of CH4 releases 802.2 kJ of energy.

    • When you make 802.2 kJ you also make 2 moles of water


Thermochemistry

  • The magnitude of ΔH is directly proportional to the amount of reactants or products.

  • 1A + 2 B ----> 1CΔH = -100 kJ

  • 1/2 A + 1B ----> 1/2 CΔH = -50 kJ


Ch 4 2o 2 co 2 2h 2 o h 802 2 kj

CH4 + 2O2® CO2 + 2H2O; ΔH = -802.2 kJ

Rewrite chemical equation as a thermochemical equation.

Exothermic or endothermic reaction?

If 3 moles of O2 react with excess CH4 how much heat will be produced?


1 ch 4 g 2 o 2 g co 2 g 2 h 2 o l 802 2 kj

1CH4(g) + 2 O2(g)® CO2(g) + 2 H2O(l) + 802.2 kJ

  • If 10. 3 grams of CH4 are burned completely, how much heat will be produced?

Convert moles to desired unit

Convert to moles

Start with known value

1 mol CH4

802.2 kJ

10. 3 g CH4

16.05 g CH4

1 mol CH4

= 514 kJ

Ratio from balanced equation

ΔH = -514 kJ, which means the heat is released for the reaction of 10.3 grams CH4


4 no g 6 h 2 o l 4 nh 3 g 5 o 2 g h 1170 kj

4 NO(g) + 6 H2O(l)  4 NH3(g) + 5 O2(g)    ΔH = +1170 kJ

  • Based upon the thermochemical equation given, calculate the heat associated with the decomposition of 1.15 g of NO.


2 c 2 h 6 g 7 o 2 g 4 co 2 g 6 h 2 o l h 3120 kj

2 C2H6(g) + 7 O2(g)  4 CO2(g) + 6 H2O(l)   ΔH = -3120 kJ

  • Calculate the mass of ethane, C2H6, which must be burned to produce 100 kJ of heat.


Heat of reaction1

Heat of Reaction

CaO(s) + H2O(l)  Ca(OH)2(s) ΔH = -65.2 kJ

CaO + H2O

Enthalpy (H)

ΔH = -65.2 kJ

Ca(OH)2


  • Login