IB chemistry topic 7 practice questions

Which statement about chemical equilibria implies they are dynamic?

• The position of equilibrium constantly changes.

• The rates of forward and backward reactions change.

• The reactants and products continue to react.

• The concentrations of the reactants and products continue to change.

The reaction below represents the Haber process for the industrial production of ammonia.
 $N_{2\ }+\ 3\ H_{2\ }\Longleftrightarrow\ 2NH_3\ \ \ \ \ \Delta H=-92\ \frac{kJ}{mol}$  
The optimum conditions of temperature and pressure are chosen as a compromise between those that favour a high yield of ammonia and those that favour a fast rate of production. Economic considerations are also important. Which statement is correct?

• A higher temperature would ensure a higher yield and a faster rate.

• A lower pressure would ensure a higher yield at a lower cost.

• A lower temperature would ensure a higher yield and a faster rate.

• A higher pressure would ensure a higher yield at a higher cost.

Tags

NGSS.HS-PS1-5

NGSS.HS-PS1-6

 $2H_{2\ }(g)+CO\ (g)\ \Longleftrightarrow CH_3OH\ (l)\ \ \ \ \Delta\ H=−128\ \frac{kJ}{mol}$  

What is the effect of an increase of temperature on the yield and the equilibrium constant for the
following reaction?

• Yield: increases; K: increases

• Yield: increases; K: decreases

• Yield: decreases; K: increases

• Yield: decreases; K: decreases

Consider the equilibrium between methanol, CH3OH(l), and methanol vapour, CH3OH(g).
 $CH_3OH\ (l)\ \Longleftrightarrow\ CH_3OH\ (g)$  
What happens to the position of equilibrium and the value of  $K_c$   as the temperature decreases?

• Position of equilibrium shifts to the left,   $K_c$  decreases.

• Position of equilibrium shifts to the left,   $K_c$  increases.

• Position of equilibrium shifts to the right,   $K_c$  decreases.

• Position of equilibrium shifts to the right,   $K_c$  increases.

 $I_2\ (g)+Br_2\ (g)\ \Longleftrightarrow\ 2IBr\ (g)$  

0.50 mol of I2(g) and 0.50 mol of Br2(g) are placed in a closed fl ask. The following equilibrium is
established.

The equilibrium mixture contains 0.80 mol of IBr(g). What is the value of  $K_c$  ?

• 0.64

• 1.3

• 2.6

• 64

 $PCl_5\ (s)\ \Longleftrightarrow\ PCl_3\ (l)+Cl_2\ (g)$  

An increase in temperature increases the amount of chlorine present in the following equilibrium.

What is the best explanation for this?

• The higher temperature increases the rate of the forward reaction only.

• The higher temperature increases the rate of the reverse reaction only.

• The higher temperature increases the rate of both reactions but the forward reaction isaffected more than the reverse.

• The higher temperature increases the rate of both reactions but the reverse reaction isaffected more than the forward.

Tags

NGSS.HS-PS1-5

Consider the following reversible reaction. $Cr_2O_7^{2-}\ (aq)+H_2O\ (l)\ \Longleftrightarrow\ 2CrO_4^{2-}\ (aq)+2H^+\ (aq)$ What will happen to the position of equilibrium and the value of  $K_c$   when more  $H^+$   ions are added at constant temperature?

• Position of equilibrium shifts to the left;  $K_c$  decreases.

• Position of equilibrium shifts to the right;  $K_c$  increases.

• Position of equilibrium shifts to the right;  $K_c$  does not change.

• Position of equilibrium shifts to the left;  $K_c$  does not change.

Tags

NGSS.HS-PS1-5

Consider this equilibrium reaction in a sealed container:
 $H_2O\ (g)\ \Longleftrightarrow\ H_2O\ (l)$  
What will be the effect on the equilibrium of increasing the temperature from 20 °C to 30 °C?

• More of the water will be in the gaseous state at equilibrium.

• More of the water will be in the liquid state at equilibrium.

• At equilibrium the rate of condensation will be greater than the rate of evaporation.

• At equilibrium the rate of evaporation will be greater than the rate of condensation.

Tags

NGSS.HS-PS1-5

Which statement is correct for the equilibrium:

 $H_2O\ \left(l\right)\ \Longleftrightarrow\ H_2O\ \left(g\right)$  
in a closed system at 100 °C?

• All the H2O(l) molecules have been converted to H2O(g).

• The rate of the forward reaction is greater than the rate of the reverse reaction.

• The rate of the forward reaction is less than the rate of the reverse reaction.

• The pressure remains constant.