Eastleigh College Chemical Changes & Orders of Reaction Discussion

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2. (a) State Hess’ Law

(b) Briefly explain the law using one example.

(c).

(d)



3. (a) Define Δ Hθr Δ Hθc and Δ Hθf including the standard conditions.

(b) 50 grams of sand was heated, receiving 2220J as the water. Its temperature changed from 22.3 degree Celsius to 75.8 degree Celsius. What is the specific heat capacity of the sand?

Note- Specific heat capacity is 4.18 in case of water only.

(c)

Note- 100 cm3 is equal to 100 grams of water

(d) 34.5g of sodium chloride is dissolved in water. Temperature decreases from 301K to 298K. Total mass of the solution was 980g. Calculate the standard enthalpy change of reaction. The balanced reaction involves 3 moles of sodium chloride.




4. The table below shows the results of a series of initial rate experiments for the reaction



2NO (g) + Cl2 (g) 2 NOCl (g)



Experiment

[NO]

(mol/dm3)

[Cl2]

(mol/dm3)

Initial rate

(mol/dm3s)

1

0.125

0.125

1.79 x 10 -7

2

0.250

0.125

7.16 x 10 -7

3

0.250

0.250

1.43 x 10 -6



(a) Define the rate determining step.



(b) Explain which molecules take part in the rate determining step in the above reaction and the order of reaction with respect to these molecules.



(c) Write a rate equation for this reaction (including units) and determine the value of the rate constant at this temperature.

5. A reaction is given as 2A + B = 2C + D. What is the overall order of reaction? What does the order tell you?

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Explanation & Answer

Hello! Attached are the answers to your assignment. Do let me know if you have any questions/need revisions :)I just want to let you know that some questions contain inappropriate data given, so I did my best to address them, like finding a similar problem with a more appropriate dataset or make an assumption regarding the problem itself.

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Chemistry
Chemical Changes & Orders of Reaction

1. With the aid of fully labelled diagrams, explain the terms exothermic and
endothermic.
An exothermic reaction is a reaction in which the overall standard enthalpy change of
reaction (ΔrxnH) is negative.
ΔrxnH = ΔfHproducts – ΔfHreactants < 0
Exothermic reactions release heat and entail the replacement of weak bonds with
stronger ones. These reactions increase the temperature of their surrounding area,
thereby creating a heating effect.

An endothermic reaction is any reaction with an increase in the enthalpy H of the
system.
ΔrxnH = ΔfHproducts – ΔfHreactants > 0
Endothermic reactions are chemical reactions in which the reactants absorb heat
energy from the surroundings to form products. These reactions lower the temperature
of their surrounding area, thereby creating a cooling effect.

2. (a) Write the equation for rate law including rate constant? What are the units of k for
the rate law: Rate = k[A][B]2, when the concentration unit is mol/dm3?
Rate law of a unimolecular reaction with an order of n:
𝑟 = 𝑘[𝐴]𝑛
−1 1−𝑛 −1
Rate constant unit with n rate order: 𝑘 = (𝑚𝑜𝑙 𝐿 ) 𝑠

For the rate law 𝑣 = 𝑘[𝐴][𝐵]2 the reaction rate order is equal to 3, hence:
𝑘 = (𝑚𝑜𝑙 𝐿−1 )(1−3) 𝑠 −1
= (𝑚𝑜𝑙 𝐿−1 )−2 𝑠 −1
= 𝒎𝒐𝒍−𝟐 𝑳𝟐 𝒔−𝟏
(b) Consider the ...


Anonymous
Excellent resource! Really helped me get the gist of things.

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