Reversible reaction problem

Question

1) What would happen to the amount of products formed in the following equilibrium in the following circumstances (explain your answers)? The forward reaction is endothermic.

 

CH4(g) + H2O(g) ? CO(g) + 3 H2(g)

 

a) What would happen, and why, if the temperature was increased? (3) b) What would happen, and why, if the pressure was increased? (3)

c) What would happen, and why, if more steam was added? (3) 2) Yellow chromate ions are in equilibrium with orange chromate ions.

 

2 CrO42-(aq) + 2 H+(aq) ? Cr2O72-(aq) + H2O(l) yellow orange

 

a) What would happen, and why, if acid was added to a yellow solution of chromate ions? 

 

b) What would happen and why if alkali was added to a yellow solution of chromate ions? 

 

3) Ethanoic acid is a weak acid. Some ethanoic acid and universal indicator were placed in a flask.

CH3COOH(aq) ? CH3COO-(aq) + H+(aq) colourless colourless

 

a) What colour would the universal indicator be?

 

 b) What would happen to the colour and why if some sodium ethanoate was added? 

Answer 1

It is important to remember in chemical reactions that anything that puts pressure on one side of the equation will drive the reaction in the other direction.

1) CH4(g) + H2O(g) ? CO(g) + 3 H2(g)

a) If the temperature is increased...

     The problem states that the reaction is endothermic.  That basically means it requires heat to move forward (as opposed to exothermic reactions, which give off heat).  In the case of endothermic reactions, it is helpful to think of heat as one of the reactants.  Basically, if we are increasing the temperature, it will have the same effect as increasing the concentration of a reactant, and it will increase the amount of product formed.

b)If the pressure was increased...

Both the reactants and products are gasses, but there are only 2 moles of reactant (1 CH4 and 1 H20) where there are 4 moles of product (1 Co and 3 H2).  Putting more pressure on the container will force the reaction in the direction that has less moles of gas, so it would cause less products.

c)... if you added steam

Adding steam = adding H20 so we are adding a reactant.  This will cause an increase in product creation.