Question

Systems that have gaseous reactants and products behave a little bit differently when an experimenter works to force the system out of equilibrium in order to obtain a product. The mechanism of stress that is used is "pressure". [If you need to review this concept a little bit it can be found in Lesson 7.4 - Changing Reaction Rates. Guided notes might help support you, or even reviewing Unit 6 Rates of Reaction Lesson 2 a little bit. --- I am certain you can work through this!]

Added pressure, or force exerted over area, can increase the number of collisions among particles in a closed system. Hopefully this makes sense. The system works to balance numbers of 'moles' of reactant(s) and product(s) throughout. We can find the number of moles by BALANCING the EQUATION. Here is our example from the Haber-Bosch process we used in Unit 6 portfolio work. It explains 'why' the reaction is more efficient at lower temperatures.

N2(g) + 3H2(g) ⇌ 2NH3 (g) + heat energy

nitrogen gas + hydrogen gas react reversibly to form ammonia gas + heat



Please use the image above to help you count moles of reactants and products to determine which direction the shift will take the experimenter under the conditions applied. The equation is balanced for you.





(6 points)
Forward Reaction (shift right) Reverse Reaction (shift left)
The experiment counts 8 moles of ammonia in the closed system.


The experimenter REMOVES heat from the closed system.


The experimenter counts 1 mole of ammonia in the closed system.


The experimenter counts 2 moles of nitrogen and 6 moles of hydrogen gas in the closed system.


The experimenter ADDS the catalyst of iron to break the triple covalent bonds in nitrogen gas. [Check Lesson 7.4 for help if needed!]


The experimenter ADDS heat to the closed system.

Answer 1

1) The experiment counts 8 moles of ammonia in the closed system. — Shift left (reverse).
Reason: excess product drives the reaction back toward reactants.

2) The experimenter REMOVES heat from the closed system. — Shift right (forward).
Reason: reaction is exothermic (heat on product side); removing heat shifts equilibrium to produce heat (forward).

3) The experimenter counts 1 mole of ammonia in the closed system. — Shift right (forward).
Reason: low product concentration causes the system to make more product.

4) The experimenter counts 2 moles of nitrogen and 6 moles of hydrogen gas in the closed system. — Shift right (forward).
Reason: adding reactants (or having an excess of reactant moles) drives the reaction toward products.

5) The experimenter ADDS the catalyst of iron to break the triple covalent bonds in nitrogen gas. — No shift (no change in position).
Reason: a catalyst speeds both forward and reverse rates equally and does not change equilibrium.

6) The experimenter ADDS heat to the closed system. — Shift left (reverse).
Reason: adding heat favors the endothermic direction (left) to absorb the added heat.