a pure solid sample of substance x is put into an evacuated flask. the flask is heated at a steady rate and the temperature recorded as time passes. here is graph of the results: use this graph to answer the following questions: what is the melting point of x? \boxed{} ^\circ c what phase (physical state) of x would you expect to find in the flask after 22 kj/mol of heat has been added? (check all that apply) \square solid \square liquid \square gas

Question

Accepted Answer

### First Question: Melting Point of X
# Explanation:
## Step1: Identify Melting Region
On a heating curve, the melting point is where the temperature is constant during melting (solid to liquid phase change). The flat segment (horizontal line) on the graph represents the phase change (melting here).
## Step2: Read Temperature at Flat Segment
Looking at the graph, the flat part (melting) occurs at a temperature of 100 °C (from the y - axis, temperature scale). So the melting point is the temperature at this flat segment.
# Answer:
100

### Second Question: Phase after 22 kJ/mol Heat
# Explanation:
## Step1: Analyze Heat Added vs. Phase Changes
First, the melting occurs at the first flat segment. Then, after melting, the temperature rises (liquid heating) until the next flat segment (boiling). The heat added of 22 kJ/mol: after melting (the first flat segment ends before 20 kJ/mol? Wait, looking at the x - axis (heat added, kJ/mol), 22 kJ/mol is after the melting (first flat) and before the boiling (second flat). Wait, no, let's re - check: the first flat is melting (solid to liquid), then temperature rises (liquid), then second flat is boiling (liquid to gas). At 22 kJ/mol, we are in the region where the temperature is rising after melting (so liquid) or before boiling? Wait, the graph: after the first flat (melting), the temperature increases (liquid heating) until the second flat (boiling). So at 22 kJ/mol, which is after the melting (first flat) and before the boiling (second flat), the substance is liquid? Wait, no, wait the second flat: when does the second flat start? The x - axis: the first flat is from 0 to around 5 kJ/mol? No, the graph: the first flat (melting) is at low heat, then temperature rises (liquid), then second flat (boiling) at higher heat. Wait, the heat added at 22 kJ/mol: looking at the x - axis, the second flat (boiling) starts around 20 kJ/mol? Wait, the graph shows that after the first flat (melting), the temperature rises (liquid) until the second flat (boiling) starts. So at 22 kJ/mol, which is in the second flat? Wait, no, the second flat is the boiling (liquid to gas). Wait, maybe I misread. Let's see: the first horizontal line (melting, solid - liquid) at around 100 °C, then temperature rises (liquid heating) to the next horizontal line (boiling, liquid - gas) at a higher temperature. The heat added at 22 kJ/mol: if the second flat (boiling) starts at around 20 kJ/mol? Wait, the x - axis: the first flat is from 0 to ~5 kJ/mol (melting), then temperature rises (liquid) until ~20 kJ/mol, then second flat (boiling) from ~20 to ~30 kJ/mol? Wait, no, the graph as per the user: the first flat (melting) at low heat, then temperature rises (liquid) to the second flat (boiling) at higher heat. So at 22 kJ/mol, we are in the second flat? No, the second flat is where temperature is constant (boiling, liquid and gas co - exist). Wait, no, when heat is added during boiling, temperature is constant (liquid to gas). So if 22 kJ/mol is in the second flat (boiling), then both liquid and gas? But the options are solid, liquid, gas. Wait, no, maybe the first flat is melting (solid - liquid), then temperature rises (liquid) until the second flat (boiling, liquid - gas). So at 22 kJ/mol, if the second flat starts at 20 kJ/mol, then at 22 kJ/mol, we are in the boiling phase (liquid and gas). But wait, the problem says "after 22 kJ/mol of heat has been added". Wait, maybe the second flat is the boiling, so at 22 kJ/mol, which is in the second flat (boiling), so the phase is liquid and gas? But the options are solid, liquid, gas (check all that apply). Wait, no, let's re - examine the graph:

- First flat: melting (solid → liquid, heat added: low, temperature 100 °C)
- Then temperature rises (liquid, heat added increasing, temperature increasing)
- Second flat: boiling (liquid → gas, heat added increasing, temperature constant)

So when heat added is 22 kJ/mol, which is in the second flat (boiling), so the substance is in liquid and gas phase? But the options are solid, liquid, gas. Wait, maybe I made a mistake. Wait, the first flat: melting (solid to liquid), then temperature rises (liquid), then second flat: boiling (liquid to gas). So at 22 kJ/mol, if the second flat starts at 20 kJ/mol, then at 22 kJ/mol, we are in the boiling process, so both liquid and gas are present? But the options are solid, liquid, gas. Wait, no, maybe the second flat is not boiling but something else. Wait, the problem says "a pure solid sample... heated at a steady rate". So the first flat is melting (solid - liquid), second flat is boiling (liquid - gas). So after melting (first flat), the substance is liquid (when heat is added between melting and boiling). Wait, maybe the heat added at 22 kJ/mol is after the melting (first flat) and before the boiling (second flat), so the substance is liquid? Wait, no, the x - axis: the first flat (melting) is at heat added from 0 to, say, 5 kJ/mol, then temperature rises (liquid) until heat added of 20 kJ/mol, then second flat (boiling) from 20 to 30 kJ/mol. So at 22 kJ/mol, which is in the second flat (boiling), so the substance is liquid and gas. But the options are solid, liquid, gas. So we check liquid and gas? Wait, no, maybe I misread the graph. Alternatively, maybe the second flat is not boiling but the end of heating? No, the graph shows a third part? Wait, the original graph: the y - axis is temperature (°C), x - axis is heat added (kJ/mol). The first horizontal line (melting, solid - liquid), then temperature rises (liquid), then second horizontal line (boiling, liquid - gas). So at 22 kJ/mol, which is in the second horizontal line (boiling), so the phase is liquid and gas. But the options are solid, liquid, gas. So we check liquid and gas? But maybe the heat added at 22 kJ/mol is in the liquid phase (before boiling). Wait, maybe the second flat starts at 30 kJ/mol. Let's re - look: the x - axis goes up to 40 kJ/mol. The first flat is at low heat (0 - 5 kJ/mol), then temperature rises (5 - 20 kJ/mol, liquid), then second flat (20 - 30 kJ/mol, boiling), then temperature rises (gas). So at 22 kJ/mol, which is in the second flat (20 - 30 kJ/mol), so the phase is liquid and gas. But the options are solid, liquid, gas. So we check liquid and gas? But the problem says "check all that apply". Wait, maybe I made a mistake. Wait, the first flat: melting (solid to liquid), so after melting, the substance is liquid (when heat is added between melting and boiling). So if 22 kJ/mol is after melting (first flat) and before boiling (second flat), then it's liquid. But if the second flat starts at 20 kJ/mol, then 22 kJ/mol is in the second flat (boiling), so liquid and gas. This is a bit confusing, but based on typical heating curves:

- Melting: solid → liquid (temperature constant)
- Liquid heating: temperature rises (liquid)
- Boiling: liquid → gas (temperature constant)

So the heat added at 22 kJ/mol: if the boiling starts at 20 kJ/mol, then at 22 kJ/mol, we are in boiling (liquid and gas). But maybe the graph's second flat starts at 20 kJ/mol, so at 22 kJ/mol, the phase is liquid and gas. But the options are solid, liquid, gas. So we check liquid and gas? Wait, no, maybe the second flat is not boiling but the end of the liquid heating. Wait, the user's graph: the first flat (melting) at ~100 °C, then temperature rises to ~180 °C, then flat again. So the first flat: melting (solid - liquid), second flat: boiling (liquid - gas). So at 22 kJ/mol, which is in the second flat (boiling), so the phase is liquid and gas. But the options are solid, liquid, gas. So we check liquid and gas? But maybe the answer is liquid? Wait, no, when boiling, both liquid and gas are present. But the problem says "check all that apply". So we need to see:

After 22 kJ/mol heat:

- Solid: No, because melting has already occurred (first flat is melting, so solid has melted).
- Liquid: Yes, because boiling is liquid to gas, so liquid is still present.
- Gas: Yes, because boiling is occurring (liquid to gas), so gas is present.

Wait, but maybe the second flat is not boiling but the end of the liquid phase. No, in a heating curve, the flat segments are phase changes (melting and boiling). So the correct phases are liquid and gas. But let's confirm with the heat added:

- Melting: occurs at low heat (first flat)
- Liquid heating: heat added after melting, temperature rises (liquid)
- Boiling: heat added at higher heat, temperature constant (liquid and gas)

So at 22 kJ/mol, which is in the boiling phase (second flat), so liquid and gas are present. So we check liquid and gas.

# Answer:
liquid, gas (check the boxes for liquid and gas)

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QUESTION IMAGE

Question

Explanation:

First Question: Melting Point of X

Step1: Identify Melting Region

Step2: Read Temperature at Flat Segment

Step1: Analyze Heat Added vs. Phase Changes

Answer:

Second Question: Phase after 22 kJ/mol Heat