Question

(c) (i) state two effects of heat on a substance. (ii) by how much should water of temperature -25 °c be increased to obtain its freezing point temperature? 4 marks

Explanation:

(c)(i)

Step1: Recall heat and substance

Heat impacts a substance's temperature (kinetic energy) and phase (potential energy, like melting/freezing, boiling/condensing). So, heat affects a substance by changing its temperature (when phase is constant) and its physical state/phase (when temperature is constant, e.g., melting, boiling).

Step1: Identify freezing point of water

The freezing point of water (at standard pressure) is \(0^\circ \text{C}\).

Step2: Calculate temperature increase

We need to find the difference between the freezing point (\(0^\circ \text{C}\)) and the initial temperature (\(-25^\circ \text{C}\)).
The formula for temperature increase \(\Delta T = T_{\text{final}} - T_{\text{initial}}\).
Substitute \(T_{\text{final}} = 0^\circ \text{C}\) and \(T_{\text{initial}} = -25^\circ \text{C}\):
\(\Delta T = 0 - (-25) = 0 + 25 = 25^\circ \text{C}\).

Answer:

Heat on a substance changes its \(\boldsymbol{\text{temperature}}\) (kinetic energy of particles) and its \(\boldsymbol{\text{physical state/phase}}\) (potential energy, e.g., melting, boiling).

(c)(ii)