Question

question 3 (1 point)
use le chateliers principle to decide what happens to the ph₃. all are gases.
4 ph₃ + 2 h₂ + 9 o₂ ↔ 2 p₂o₅ + 8 h₂o + 25 kj
ph₃ 1 when h₂o is increased
ph₃ 2 when h₂o is decreased
ph₃ 3 when o₂ is increased
ph₃ 4 when o₂ is decreased
a. increases b. decreases c. is changed

Explanation:

Step1: Analyze [H₂O] increase

Le Chatelier's Principle: If a product (H₂O) concentration increases, the equilibrium shifts left (reverse reaction) to consume excess product. So, more PH₃ is produced (since reverse reaction makes reactants). Thus, [PH₃] increases? Wait, no: Wait, the reaction is 4 PH₃ + 2 H₂ + 9 O₂ ⇌ 2 P₂O₅ + 8 H₂O + 25 kJ. So H₂O is a product. Increasing [H₂O] (product) shifts equilibrium left (towards reactants). So PH₃ is a reactant; shifting left means more reactants, so [PH₃] increases? Wait, no: Wait, when you add a product, the reaction goes backward (reverse), so reactants (PH₃, H₂, O₂) are formed. So [PH₃] increases? Wait, no, wait: Let's re-express. The forward reaction makes products (P₂O₅, H₂O). Reverse reaction makes reactants (PH₃, H₂, O₂). So if [H₂O] (product) increases, the system tries to reduce [H₂O] by going reverse: so reverse reaction (reactants formed). So PH₃ is a reactant, so reverse reaction produces PH₃? Wait, no: reverse reaction is 2 P₂O₅ + 8 H₂O → 4 PH₃ + 2 H₂ + 9 O₂. So yes, reverse reaction produces PH₃. So increasing [H₂O] (product) causes reverse reaction, so [PH₃] (reactant in forward, product in reverse) increases? Wait, no, PH₃ is a reactant in forward. So in reverse, it's a product. So when we add H₂O (product), the reaction goes reverse, so PH₃ (product of reverse) increases. So for [H₂O] increased, [PH₃] increases? Wait, no, maybe I got it wrong. Wait, Le Chatelier: if you add a product, equilibrium shifts left (towards reactants). Wait, reactants are PH₃, H₂, O₂. So shifting left means making more reactants? Wait, no: left side is reactants, right is products. So shifting left is from products to reactants. So if you have more products (H₂O), the system will convert products to reactants. So PH₃ is a reactant, so converting products to reactants means producing PH₃? Wait, no, the reverse reaction is products → reactants. So reverse reaction: P₂O₅ + H₂O → PH₃ + H₂ + O₂. So in reverse, PH₃ is a product. So adding H₂O (product) causes reverse reaction, so PH₃ (product of reverse) increases. So [PH₃] increases when [H₂O] increases? Wait, no, maybe I messed up. Let's take a simple example: A + B ⇌ C + D. If [D] increases, equilibrium shifts left (A + B formed). So A and B are reactants, so their concentrations increase. So in our case, reactants are PH₃, H₂, O₂; products are P₂O₅, H₂O. So adding H₂O (product) shifts left, so reactants (PH₃, H₂, O₂) increase. So [PH₃] increases when [H₂O] increases. Wait, but the options are A. increases, B. decreases, C. is changed. Wait, maybe I made a mistake. Wait, no: Let's do step by step.

Step1: [H₂O] increased

Reaction: 4 PH₃ + 2 H₂ + 9 O₂ ⇌ 2 P₂O₅ + 8 H₂O + 25 kJ. H₂O is a product. According to Le Chatelier, increasing a product's concentration shifts equilibrium to the left (towards reactants) to consume the excess product. Shifting left means the reverse reaction (products → reactants) is favored. So reactants (PH₃, H₂, O₂) are produced. Thus, [PH₃] increases? Wait, no, PH₃ is a reactant, so producing reactants means [PH₃] increases. So for [H₂O] increased, [PH₃] increases (A)? Wait, but let's check the next step.

Step2: [H₂O] decreased

Decreasing [H₂O] (product) shifts equilibrium to the right (forward reaction) to produce more H₂O. Forward reaction consumes reactants (PH₃, H₂, O₂) to make products. So [PH₃] (reactant) decreases? Wait, no: forward reaction is 4 PH₃ + ... → ... + 8 H₂O. So if we need to make more H₂O (because [H₂O] decreased), the forward reaction is favored, so reactants (PH₃) are consumed, so [PH₃] decreases? Wait, no: Wait, decreasing a product (H₂O) causes the system to make more product (forward reaction), so reactants are used up, so [PH₃] decreases? Wait, no, let's re-express. If [H₂O] is decreased, the system tries to increase [H₂O] by going forward (making more H₂O). Forward reaction uses PH₃ (reactant), so [PH₃] decreases? Wait, no, forward reaction consumes PH₃, so [PH₃] decreases? Wait, no, if forward reaction is favored, reactants are consumed, so [PH₃] decreases. So when [H₂O] is decreased, [PH₃] decreases? Wait, no, maybe I got it reversed. Wait, let's use the simple A + B ⇌ C + D. If [D] decreases, equilibrium shifts right (A + B → C + D), so A and B (reactants) are consumed, so [A] decreases. So in our case, [H₂O] (D) decreases, so equilibrium shifts right (forward), so PH₃ (A) is consumed, so [PH₃] decreases? Wait, no, that can't be. Wait, no: in the simple reaction, A is a reactant. If equilibrium shifts right (forward), A is consumed, so [A] decreases. So in our problem, when [H₂O] (product) decreases, forward reaction is favored (to make more H₂O), so reactants (PH₃) are consumed, so [PH₃] decreases? Wait, but that contradicts the first step. Wait, maybe I made a mistake in step 1. Let's re-examine step 1: [H₂O] increased (product), so equilibrium shifts left (reverse), so reactants (PH₃) are produced (since reverse reaction is products → reactants, so PH₃ is a reactant, so reverse reaction produces PH₃? Wait, no, reverse reaction is 2 P₂O₅ + 8 H₂O → 4 PH₃ + 2 H₂ + 9 O₂. So in reverse, PH₃ is a product. So when we add H₂O (product), reverse reaction happens, so PH₃ (product of reverse) increases. So [PH₃] increases when [H₂O] increases (A). When [H₂O] decreases, forward reaction happens (to make more H₂O), so PH₃ (reactant in forward) is consumed, so [PH₃] decreases (B)? Wait, no, B is "decreases". Wait, but let's check O₂.

Step3: [O₂] increased

O₂ is a reactant. Increasing a reactant's concentration shifts equilibrium to the right (forward reaction) to consume the excess reactant. Forward reaction consumes PH₃ (reactant) to make products. So [PH₃] decreases (B)? Wait, no: forward reaction is 4 PH₃ + ... → ..., so consuming PH₃, so [PH₃] decreases. So when [O₂] (reactant) increases, equilibrium shifts right, so [PH₃] (reactant) decreases (B).

Step4: [O₂] decreased

O₂ is a reactant. Decreasing a reactant's concentration shifts equilibrium to the left (reverse reaction) to produce more reactant. Reverse reaction produces PH₃ (as in step 1), so [PH₃] increases (A).

Wait, let's summarize:

1. [H₂O] increased (product): shift left (reverse), produce PH₃ → [PH₃] increases (A)
2. [H₂O] decreased (product): shift right (forward), consume PH₃ → [PH₃] decreases (B)
3. [O₂] increased (reactant): shift right (forward), consume PH₃ → [PH₃] decreases (B)
4. [O₂] decreased (reactant): shift left (reverse), produce PH₃ → [PH₃] increases (A)

Wait, but let's confirm with Le Chatelier's Principle:

- For a product (H₂O):
- Increase: shift left (reverse) → reactants (PH₃) increase (A)
- Decrease: shift right (forward) → reactants (PH₃) decrease (B)
- For a reactant (O₂):
- Increase: shift right (forward) → reactants (PH₃) decrease (B)
- Decrease: shift left (reverse) → reactants (PH₃) increase (A)

So the answers should be:

1. A (increases)
2. B (decreases)
3. B (decreases)
4. A (increases)

But let's check the options:

A. increases

B. decreases

C. is changed

So:

1. When [H₂O] is increased: A

2. When [H₂O] is decreased: B

3. When [O₂] is increased: B

4. When [O₂] is decreased: A

Answer:

1. A. increases
2. B. decreases
3. B. decreases
4. A. increases