Hannah does an experiment. She has two colorless chemicals that she mixes together in a beaker. Which of the following indicates that a chemical change occurs when she mixes the two chemicals together?
I. The chemicals change color from colorless to purple.
II. A yellow gas forms.
III. A brown solid forms in the bottom of the beaker.
IV. The temperature of the chemicals rises 15°C.

A. II and III only
B. I, II, III, and IV
C. I and III only
D. I, II, and III only

Question

Hannah does an experiment. She has two colorless chemicals that she mixes together in a beaker. Which of the following indicates that a chemical change occurs when she mixes the two chemicals together?
I. The chemicals change color from colorless to purple.  
II. A yellow gas forms. 
III. A brown solid forms in the bottom of the beaker. 
IV. The temperature of the chemicals rises 15°C. 
 
  A.   II and III only  
  B.   I, II, III, and IV 
 C.   I and III only  
  D.   I, II, and III only

zale101 · Answer

How to know if chemical change occurs if:
Sounds and light is giving off, change of smell or color when gases or precipitations are formed, and change in temperature/energy when it undergoes an exothermic (gain of heat) and endothermic (loss of heat)

anonymous · Answer

Zale101
So it's B. I, II,III and IV?

anonymous · Answer

When a strip of zinc metal is added to a test tube of hydrochloric acid, the liquid forms bubbles, and the test tube feels hot. The bubbles are a result of the formation of hydrogen gas. What does the hot test tube indicate?  

  A.    Hydrogen gas is removing heat.  
  B.   an endothermic reaction  
  C.   an exothermic reaction  
  D.    Hydrogen gas is hot.

anonymous · Answer

Which of the following statements is true?  

  A.    Chemical reactions can only absorb heat energy.  
  B.    Chemical reactions can neither absorb heat energy nor release heat energy.  
  C.    Chemical reactions can either absorb heat energy or release heat energy.  
  D.    Chemical reactions can only release heat energy.

anonymous · Answer

A piece of metal is dropped into a solution of acid. Using a sharp probe, the metal is broken into smaller pieces while in the solution. Also while in the solution, some of the metal reacts, producing hydrogen gas. Which statement is true about the changes that have occurred?  

  A.    Only chemical changes have occurred.  
  B.    Only physical changes have occurred.  
  C.    Physical and chemical changes have occurred.  
  D.    No physical or chemical changes have occurred.

anonymous · Answer

@Kryten

triciaal · Answer

C. an exothermic reaction

triciaal · Answer

read the post by @Zale101
C. Chemical reactions can either absorb heat energy or release heat energy.

triciaal · Answer

C. Physical and chemical changes have occurred. 
metal is broken into smaller pieces    physical
some of the metal reacts, producing hydrogen gas   chemical