A substance undergoes a change. Which of the following indicates that the change was a chemical change?
2 answers:
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Explanation:
- Evaporation is defined as a process in which liquid state of water is changing into vapor state.
So, we need to break the bonds of liquid substance in order to convert it into vapor state. And, energy is absorbed for breaking of bonds which means that evaporation is an endothermic process.
Hence, the statement evaporation of water is an exothermic process is false.
- When a hydrocarbon reacts with oxygen and leads to the formation of carbon dioxide and water then this type of reaction is known as combustion reaction.
A combustion reaction will always release heat energy. Hence, combustion reaction is exothermic in nature.
- When energy is transferred as heat from the surroundings to the system then it means energy is being absorbed by the system. And, absorption of heat is an endothermic process for which
is positive.
- Whereas when energy is transferred from system to the surrounding then it means energy is released by the system which is an exothermic process.
Hence, for an exothermic process value of is negative.
Thus, we can conclude that statements which are true are as follows.
- A combustion reaction is exothermic.
- When energy is transferred as heat from the system to the surroundings,
- For an endothermic reaction Deta H is positive.
Answer:
Observe odor, determine pH, determine density, determine boiling point
Explanation:
The correct procedures that would be best to use to determine whether a beaker contains only distilled water would be to observe the odor of the liquid in the beaker, determine the pH of the liquid, determine the density, and then determine the boiling point of the liquid.
<em>Water is generally odorless and has a pH of approximately 7 with a density of 1 kg/m3 and a boiling point of 100 </em><em>. If the liquid in the beaker ticks all these conditions, then it can be established to be only distilled water.</em>