4. PRO Chemical Changes

Consider the following questions that might be posed in a chemistry context:

  1. Why does fizzing occur when vinegar is added to baking soda?

  2. Why does a hand warmer heat up when activated?

  3. Why does a precipitate form when lead nitrate and potassium iodide are mixed?

  4. Why does iron rust when exposed to water and oxygen?

  5. Why does a magnesium strip burn with a bright white flame?

  6. Why does methane need a spark or flame to start burning?

  7. Why does copper carbonate break down when it is heated?

  8. How do plants make glucose?

  9. Why does magnesium fizz in hydrochloric acid?

  10. Why does copper develop a green coating outdoors?

  11. Why does a white solid form when silver nitrate and sodium chloride are mixed?

  12. Why does ethanol undergo combustion?

  13. Why does a bright white flame occur when magnesium burns?

For each question, write a complete PRO explanation using the structure below.

Ensure:

  • The Premise (P): states a general scientific principle or condition.

  • The Reasoning (R): explains the mechanism linking cause to effect.

  • The Outcome (O): states the observable result.

Choose from the PRO starters below to structure the explanations.

Premise (P) Starters

According to the relevant scientific theory…
Under these conditions…
The governing principle is that…
According to the established model…
The underlying mechanism is that…
The principle governing this behaviour is that…
The phenomenon can be attributed to…
According to the particle model of matter…
The key scientific idea is that…
In chemical reactions, the general rule is that…
This system behaves as it does because…

Reasoning (R) Starters

At the microscopic scale…
This process leads to…
Mechanistically, this produces…
At the sub-microscopic level…
As a consequence of this increase…
This acceleration of particle motion results in…
The redistribution of energy leads to…
This elevation in kinetic energy facilitates…
At the particle level, this occurs because…
As particles collide and interact…
This involves the breaking and forming of bonds, which…
As energy is transferred within the system…
This rearrangement of particles results in…

Outcome (O) Starters

The observable effect is that…
The measurable outcome is that…
Thus, the macroscopic result is…
Ultimately, this manifests as…
Thus, the system undergoes a macroscopic change.
Hence, an observable transformation is produced.
As a result, a visible change is observed.
This results in evidence of a chemical change, such as…
The final observable outcome is that…
This can be observed as…