How Far? The Extent of Chemical Change (HL IB Chemistry)

Which systems are correctly described? 

1. Matter and energy can be transferred across the boundary of an open system
2. Only matter can be transferred across the boundary of a closed system
3. Matter and energy cannot be transferred across the boundary of an isolated system

Ethyne and hydrogen are formed from methane and a dynamic equilibrium is established.

2CH₄ (g)  ⇌   3H₂ (g) +   C₂H₂ (g)                                                 

What are the units for K_c?

The dissociation of gas X₂Y₄ into XY₂ is represented in the equation below:

X₂Y₄ (g)  ⇌  2XY₂ (g)         ${\mathrm{\Delta H}}^{\mathrm{\theta }}$ = +60 kJ mol^-1 

At constant pressure, if the temperature of the equilibrium mixture of the gases is increased, will the volume of the mixture increase or decrease and why?

The reaction between nitrogen and hydrogen produces ammonia gas:

N₂ (g) + 3H₂ (g)    2NH₃ (g)

If the equilibrium constant for the reaction is x, what is the equilibrium constant for the following reaction?

2N₂ (g) + 6H₂ (g)    4NH₃ (g)

For the following reaction at equilibrium

H₂S (aq)  +  Mg²⁺ (aq)  ⇋   MgS (s)   +  2H⁺ (aq)              ΔH < 0

Which of the following changes will result in more MgS being produced?

When a chemical reaction reaches equilibrium which of the following can be said about the concentrations of the substances present, and the rates of reaction?

The Haber process is used to produce ammonia industrially by the following reaction

N₂ (g)  +  3H₂ (g)    2NH₃ (g)

Which statements explain why a catalyst is used?

Study the following equilibrium reaction and determine which of the changes listed below will shift the equilibrium to the right hand side.

2CO₂ (g)     2CO (g)   +   O₂ (g)

Which of the following conclusions can be made about this reaction?

H₂O (g)   ⇋   H₂ (g)   + O₂ (g)            K_c = 8 x 10^-41 at 25 C

The value of K_c at 298K for the following reaction is 4.0. The reaction takes several days to react in equilibrium at room temperature.

CH₃COOH (l) +   CH₃CH₂OH (l)  ⇋  CH₃COOCH₂CH₃ (l)   +  H₂O (l)

A student carried out the reaction shown and a day later measured the concentrations and calculated a value for the reaction quotient, Q. She found that the value of Q was 8.7.

This value tells you that:

In the equilibrium reaction shown

2ICl (l)   ⇋    I₂ (g)   +   Cl₂ (g)     ΔHᶿ = -26 kJ

What will change if the temperature is lowered?

Which of these processes are endothermic?

I.  Condensing

II. Subliming

III. Melting

When gaseous dinitrogen pentoxide, N₂O₅ (g), decomposes at 358 K, the following equilibrium is established:

2N₂O₅ (g)  ⇌ 4NO₂ (g) + O₂ (g)

2.0 mol of N₂O₅ (g) were placed in a 1.0 dm³ container and allowed to reach equilibrium. At equilibrium 1.0 mol of N₂O₅ (g) were present. What is the value of K_c?

Consider the following reversible reaction:

3O₂ (g) ⇌ 2O₃ (g) 

What is the value of K_c when the equilibrium concentrations are [O₂] = 4.0 mol dm^-3 and [O₃] = 4.0 mol dm^-3 ?

Which if the following will shift the position of equilibrium to the right in the reaction  shown? 

2N₂O₅ (g)  ⇌ 4NO₂ (g) + O₂ (g)     ΔH = +219.2 kJ 

1.  Decreasing the concentration of NO₂ (g)
2.  Decreasing the temperature
3.  Decreasing the pressure

Hydrogen iodide decomposes to form hydrogen and iodine vapour.

2HI (g)  ⇌ H₂ (g) + I₂ (g)

What is the effect of decreasing the volume of the equilibrium mixture at constant temperature?

A mixture of 0.40 mol of SO₂ (g) and 0.40 mol of O₂ (g) was placed in a 1 dm³ container. The following equilibrium took place:

2SO₂ (g)  + O₂ (g) ⇌  2SO₃ (g) 

At equilibrium the mixture contained 0.25 mol of O₂ (g) .How many moles of SO₂ (g) and SO₃ (g) were present at equilibrium?

Study the following equilibrium reaction and determine which of the statements must be true.

2X    ⇋   Y               K_c = 1.1

Hydrogen reacts with iodine according to the following equation

H₂ (g)  + I₂ (g)   ⇋   2HI (g)

The value of K_c for this reaction has been measured at different temperatures

K_c  =  60  at 355 C

K_c  =  47  at 450 C

From the information given which of the following must be true?

The following K_c values were obtained for a reaction carried out at different temperatures, T₁ to T₄.

Which of the following gives the correct amount of products in the mixtures from least to most?

Which of the following conditions and reasons will increase the amount of hydrogen iodide produced?

H₂ (g)  + I₂ (g)   ⇋   2HI (g)              ΔHᶿ = -126 kJ

The blood-red complex iron (III) thiocynanate, [FeSCN]²⁺ is formed when iron (III) ions react with thiocyanate ions in the following equilibrium reaction:

Which of the following changes would make the solution go darker?

Which of the following features is not a characteristic of a state of equilibrium?

What is the relationship between K_c1 and K_c2 in the following reactions?

2NOBr (g)  ⇋   2NO (g)   +  Br₂ (g)   K_c1

NO (g)   +  Br₂ (g) ⇋  NOBr (g)   K_c2

Nitrogen dioxide can react with itself to produce a dimer molecule called dinitrogen tetroxide in the following equilibrium reaction.

2NO₂ (g)    ⇋  N₂O₄ (g)      K_c  = 0.01 at 25 C

In an experiment, 100 cm³ of nitrogen dioxide is placed in a gas syringe and the barrel is pushed in, meaning the volume is reduced to 50 cm³ at constant temperature.

Which of the following statements are true?

1. The value of Kc increases
2. More N₂O₄ is formed
3. The ratio of  decreases

One of the characteristics of a state of equilibrium, is that equilibria are said to be dynamic. What is the meaning of dynamic in this context?

The reaction shown below has a value of K_c = 1.0 x 10^-4 at 25 C.

2NOBr (g)   ⇌    2NO (g)   +  Br₂ (l)

Which of the following relationships is correct about this equilibrium at 25 C?

The Haber process is a key step in the manufacture of fertilisers:

N₂ (g) + 3H₂ (g)  2NH₃ (g)         ΔH = -ve

Which is correct about the effect of increasing temperature for this reaction?

Which equation represents a reaction where the number of moles alone can not be used to calculate the value of K_c?

When 0.20 mol NO, 0.08 mol H₂ and 0.10 mol of H₂O are placed in a 1.0 dm³ flask, the following equilibrium is established:

2NO (g) + 2H₂ (g)  N₂ (g) + 2H₂O (g)

At equilibrium, the concentration of H₂ (g) was found to be 0.02 mol dm^-3.

What is the correct value of K_c?

Nitrogen dioxide can form a dimer that can also break back down again as part of a reversible reaction:

N₂O₄ (g)  NO₂ (g)         ΔH = +ve

The reaction reaches an equilibrium at temperature T, where K_c = 1

What is true for a higher temperature, T₂?

Which would be the correct way to plot a graph and then calculate ΔG^θ from experimental data of K_c and temperature values?

ΔG^θ = -RT ln K