# Chemistry-Equilbibrium of NH4HS dissociation

• hclark91
In summary, the conversation discusses the dissociation of solid NH4HS and the calculation of Kp for the reaction. It also considers the percentage of solid dissociated when introduced into different vessels and explains the results using LeChatelier's Principle. Finally, it explores the minimum mass of solid NH4HS needed to establish equilibrium in a 2 liter flask.
hclark91

## Homework Statement

I am having trouble with this question can anyone point me in the right direction?

Solid NH4HS dissociates according to the equation:
NH4HS (s) ---> NH3 (g) + H2S (g)
SOme solid NH4HS is placed into an initially evacuated vessel and when equilibrium is established there is still some solid NH4HS left and the total pressure is 0.66 at 25 centigrade

## The Attempt at a Solution

a) calculate Kp for the reaction:

P(NH3)=(0.66 atm)/2= 0.33 atm
P(H2S)=(0.66 atm)/2= 0.33 atm
Kp=P(NH3)*P(H2S)=(0.33atm)*(0.33atm)=0.1089

b) What percent of the solid will dissociate if 0.1 mol of NH4HS is introduced inot a l liter evacuated flask at 25 centigrade:

PV=nRT
2n=PV/RT=(0.66atm)*(1L)/(0.0821 L-atm/mol-k)*(298K)=0.0269 mol
n=0.0135 mol
0.0135 mol * 51g/1mol NH4HS= 0.6879 g NH4HS .1 mol *51g/1 mol= 5.1 g
0.6879g/5.1g=0.135
0.135*100=13.5% dissociated

c) what percent of the solid will dissociate if 0.1 mol of NH4HS is introduced into a 1 liter flask that initially contains only 0.2 atm of NH3 at 25 centigrade:

NH4HS ---> NH3 + H2S
I - 0.2 0
R - +0.33n +0.33n
E - 0.2+0.33 0.33
total: 0.2+0.66n

Kp=KxPt =0.1089=(0.2+0.66n)*(0.66atm)
n=0.053
0.053 *100= 5.3% dissociated

d) Explain the results from (b) and (c) above based on LeChatelier's Principle:
LeChatelier's principle states that a system at equilibrium when subjected to a disturbance responds in a way to minimize the disturbance. The initial stress of the pressure of 0.2 atm by NH3 needed to be minimized, so less of the reactant was dissociated. Less particles in the gas phase allowed shifts the reaction toward the reactants.

e) What is the minimum mass of solid NH4HS that must be added to a 2 Liter flask in order to establish equilibrium:

I am not really sure where to go with this part. I assume I must use the gas law to find out how many moles I will need then convert it to the

Last edited:
hclark91 said:
...e) What is the minimum mass of solid NH4HS that must be added to a 2 Liter flask in order to establish equilibrium:

I am not really sure where to go with this part. I assume I must use the gas law to find out how many moles I will need then convert it to the

That is exactly how I would approach it.

Using the method I thought would work I got

PV=nRT
(0.66atm)(2L)=n(0.0821L-atm/mol-k)(298k)
n=0.5395
0.5395x51g/1mol= 2.752g of NH2HS to obtain equilibrium
does this seem right??

Look at your arithmetic. Is this true?

0.06879g/5.1g=0.135

It looks like the answer is correct but there is this 0.06879 running around, which is a bit off.

Last edited:
sorry typo

PV=nRT
2n=PV/RT=(0.66atm)*(1L)/(0.0821 L-atm/mol-k)*(298K)=0.0269 mol
n=0.0135 mol
0.0135 mol * 51g/1mol NH4HS= 0.6879 g NH4HS .1 mol *51g/1 mol= 5.1 g
0.6879g/5.1g=0.135
0.135*100=13.5% dissociated

I accidentyl put an extra 0 in 0.06879 it should be 0.6879. The rest of the numbers should be accurate after that correction

## 1. What is the definition of equilibrium in chemistry?

Equilibrium in chemistry refers to a state in which the forward and reverse reactions occur at equal rates, resulting in no overall change in the concentration of reactants and products.

## 2. How is equilibrium affected by changes in temperature?

Increasing the temperature of a reaction typically shifts the equilibrium towards the endothermic side, while decreasing the temperature shifts it towards the exothermic side. This is because an increase in temperature provides more energy for the reactants to overcome the activation energy and form products.

## 3. How does the concentration of reactants and products affect equilibrium?

The concentration of reactants and products directly affects the position of equilibrium. If there is an increase in the concentration of reactants, the equilibrium will shift to the right to form more products. Conversely, if there is an increase in the concentration of products, the equilibrium will shift to the left to form more reactants.

## 4. What is the equilibrium constant (K) and how is it calculated?

The equilibrium constant (K) is a measure of the overall ratio of products to reactants at equilibrium. It is calculated by taking the concentration of products and dividing it by the concentration of reactants, with each concentration raised to the power of its coefficient in the balanced chemical equation.

## 5. How does the dissociation of NH4HS affect equilibrium?

NH4HS (ammonium hydrosulfide) dissociates in water to form ammonium ions (NH4+) and hydrosulfide ions (HS-). The dissociation of NH4HS increases the concentration of these ions, which can then participate in other reactions and affect the equilibrium of those reactions. This is known as the common ion effect.

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