Thermal Chemistry and Energy Changes

The video reviews KCSE 2023 Chemistry Paper 2, Question 4, focusing on energy changes in physical and chemical processes. It covers heating curves, states of matter, energy cycle diagrams for potassium bromide, and bond energy calculations. The video explains how to label states of matter on a heating curve, reasons for constant temperature during phase changes, and how to calculate enthalpy changes using given thermochemical data.

What topic does Question 4 of the KCSE 2023 Chemistry Paper 2 primarily focus on?

• Nuclear Chemistry

• Organic Chemistry

• Thermal Chemistry

• Electrochemistry

In the heating curve of lead, what state is lead in between regions A and B?

• Gas

• Plasma

• Liquid

• Solid

Why does the temperature remain constant between regions B and C in the heating curve?

• The energy is lost to the surroundings.

• The substance is cooling down.

• The energy is used to convert solid to liquid.

• The substance is in a gaseous state.

What is Delta H2 in the energy cycle diagram for potassium bromide?

• Enthalpy of solution

• Lattice energy

• Bond energy

• Hydration energy

What is the role of hydration energy in the energy cycle diagram?

• It is the energy change when a solid dissolves.

• It is the energy change when a gas condenses.

• It is the energy change when water molecules surround gaseous ions.

• It represents the energy required to break bonds.

How is Delta H3 obtained from Delta H1 and Delta H2?

• Delta H3 = Delta H2 - Delta H1

• Delta H3 = Delta H1 + Delta H2

• Delta H3 = Delta H1 - Delta H2

• Delta H3 = Delta H1 * Delta H2

What is the enthalpy change for the reaction where BF3 decomposes to give B and F?

• Positive 1111 K

• Positive 237 K

• Positive 590 K

• Positive 1938 K

What is the energy change when 2 moles of F2 gas are converted to 2 moles of F gas?

• 158 K per mole

• 1111 K per mole

• 590 K per mole

• 237 K per mole

In the decomposition of BF3, what is the energy change for forming 3 moles of F?

• 237 K

• 1111 K

• 590 K

• 158 K

What is the significance of reversing the equation in the enthalpy change calculation for BF3?

• It has no effect on the energy value.

• It increases the energy required.

• It decreases the energy required.

• It changes the sign of the energy value.