Chemical changes form new substances

Steps:

• Recall that chemical changes involve breaking and forming bonds to create new substances, unlike physical changes which alter form without new products.
• Analyze the description: octane (C8H18) reacts with oxygen to produce carbon dioxide (CO2), indicating bond rearrangement.
• Evaluate options: identify which describes new substance formation versus other reaction aspects.
• Select the option tied to product formation as evidence of chemical nature.

Why D is correct:

• Chemical changes are defined by producing new substances with different properties; CO2 is a new compound from octane and oxygen, per the law of conservation of mass in reactions.

Why the others are wrong:

• A: Classifies octane as a hydrocarbon but provides no evidence of change type.
• B: Describes energy requirement for initiation, common to both chemical and physical processes like melting.
• C: Indicates reaction speed but doesn't distinguish chemical (new bonds) from physical (state change) alterations.

Final answer: D