Which of the following is a chemical change? A. Water freezing to form ice
B. Sugar dissolves in water
C. Gasoline burns in a car engine
D. A piece of metal expands when it is heated

C. would be the correct option.

Explanation:

Burning gasoline is a chemical change because when gasoline is ignited, water and carbon dioxide are produced. Water freezing to form ice would be a physical change since its state of matter has changed, but not the water itself. Sugar dissolving in water is also a physical change because all it's really doing is just forming bubbles and changing the color. Choice D. would also be a physical change since the piece of metal is still a piece of metal, it just expanded when the temperature increased.

> b takes place in the gas phase in an isothermal tubular reactor. the feed is one mole of a per one mole of c, an inert. the entering temperature and pressure are 427°c and 10 atm, respectively. the gas constant r = 0.08206 atm · l/mol · k.

the enthalpy of formation of water is given as -285.8kj/mol, which states that the enthalpy of formation is negative.

negative enthalpy of formation indicates that the heat is released during the reaction process. the heat is released from reaction to the surroundings the enthalpy is expressed with a negative sign with the energy given out in the reaction process.

the formation of water takes place by giving out heat which is -285.8 kj/mol.