Final answer:
This question asks to classify various scenarios as either physical or chemical changes. The answer provides a clear classification for each scenario, supported with explanations. The scenarios range from dissolving substances in water to reactions between different chemicals, as well as physical transformations like slicing and melting.
Step-by-step explanation:
a) Sodium hydroxide dissolves in water. - This is a physical change as the sodium hydroxide is still sodium hydroxide, it has just mixed with water to form a solution.
b) Hydrochloric acid reacts with potassium hydroxide to produce a salt, water, and heat. - This is a chemical change as new substances are formed: a salt and water, and heat is produced as a result.
c) A pellet of sodium is sliced in two. - This is a physical change as the sodium is still sodium, it has just been divided into two pieces.
d) Water is heated and changed to steam. - This is a physical change as water is still water, it has just changed from the liquid state to the gaseous state.
e) Potassium chlorate decomposes to potassium chloride and oxygen gas. - This is a chemical change as the potassium chlorate is broken down into different substances: potassium chloride and oxygen gas.
f) Iron rusts. - This is a chemical change as iron reacts with oxygen to form rust, which is a different substance.
g) When placed in water, a sodium pellet catches on fire as hydrogen gas is liberated. - This is a chemical change as the sodium reacts with water to produce hydrogen gas and heat.
h) Evaporation of alcohol. - This is a physical change as the alcohol is still alcohol, it has just changed from the liquid state to the gaseous state.
i) Ice melting. - This is a physical change as the ice is still water, it has just changed from the solid state to the liquid state.
j) Milk sours. - This is a chemical change as the milk undergoes chemical reactions, resulting in the formation of new substances and a sour taste.
k) Sugar dissolves in water. - This is a physical change as the sugar is still sugar, it has just mixed with water to form a solution.
l) Wood rots. - This is a chemical change as the wood undergoes chemical reactions, breaking down into different substances.
m) Pancakes cooking on a griddle. - This is a chemical change as the pancake batter undergoes chemical reactions, resulting in the formation of a cooked pancake.
n) Grass growing in a lawn. - This is a chemical change as the grass undergoes cellular processes to grow, resulting in the formation of new plant material.
o) A tire is inflated with air. - This is a physical change as the tire and the air are still the same substances, they have just been combined.
p) Food is digested in the stomach. - This is a chemical change as the food undergoes enzymatic reactions, breaking down into smaller molecules.
q) Water is absorbed by a paper towel. - This is a physical change as the water is still water, it has just been absorbed by the paper towel.
r) Grinding coffee beans. - This is a physical change as the coffee beans are still coffee beans, they have just been broken down into smaller pieces.
s) Shredding up your homework (please DO NOT do this). - This is a physical change as the paper is still paper, it has just been torn into smaller pieces.
t) Baking chocolate chip cookies. - This is a chemical change as the ingredients in the cookie dough undergo chemical reactions, resulting in the formation of a baked cookie.