Question

1. chefs often marinate meat in liquid before cooking to soften it and add extra flavor. a chef places a whole steak and 16 oz. of marinade in a bowl, and then marinates the mixture overnight in the refrigerator. many changes would speed up this marinating process. which change would slow it down?

a) marinating the steak at room temperature.
b) cutting the steak into pieces before marinating
c) using 16 oz. of a more concentrated marinating liquid
d) adding 16 oz. of water to the bowl, along with the marinating liquid

1. an icepack contains ammonium nitrate. when this is dissolved in water it feels much colder. this is an example of what kind of reaction?

a) exothermic
b) endothermic
c) endergonic
d) exergonic

1. which of the following is an example of a chemical reaction?

a) tearing up your last science test in frustration.
b) eating a tums to calm your upset stomach.
c) rubbing your hands together to warm them during a chilly football game.
d) pouring water on a cut to wash out any bacteria.

Explanation:

• Question 15:
• Option A: Marinating at room temperature (higher temperature) generally speeds up the process (as higher temperature increases molecular motion and reaction rates), so it's not the slowing - down option.
• Option B: Cutting the steak into pieces increases the surface area. More surface area allows for faster interaction between the marinade and the meat, speeding up the marinating process.
• Option C: A more concentrated marinade (higher reactant concentration) would speed up the marinating process (based on the principles of reaction kinetics where higher concentration leads to more frequent collisions and faster reactions).
• Option D: Adding water dilutes the marinade. A less - concentrated marinade (lower reactant concentration) slows down the marinating process (as there are fewer marinade molecules available to interact with the meat per unit volume).
• Question 16:
• Option A: An exothermic reaction releases heat. If the reaction were exothermic, the solution would feel warmer, not colder.
• Option B: An endothermic reaction absorbs heat from the surroundings. When ammonium nitrate dissolves in water and the solution feels colder, it means the reaction is absorbing heat (endothermic).
• Option C: An endergonic reaction is a reaction that requires free energy input. While endothermic reactions can be endergonic (if they also require a change in free energy), the key description here is about heat absorption (which is directly related to endothermic, not just endergonic in general).
• Option D: An exergonic reaction releases free energy. This is not related to the heat change described (feeling colder).
• Question 17:
• Option A: Tearing a paper is a physical change. It only changes the physical form of the paper (size and shape) without changing its chemical composition.
• Option B: When you eat a TUMS (calcium carbonate) to calm an upset stomach, a chemical reaction occurs. Calcium carbonate reacts with stomach acid (hydrochloric acid) to form calcium chloride, water, and carbon dioxide. The chemical composition of the substances involved changes.
• Option C: Rubbing hands together to warm them is a physical process (friction converting mechanical energy to heat). There is no change in the chemical composition of the skin or any other substances involved.
• Option D: Pouring water on a cut to wash out bacteria is a physical cleaning process. It doesn't change the chemical nature of the bacteria or the water (in terms of a chemical reaction).

Answer:

1. D. adding 16 oz. of water to the bowl, along with the marinating liquid
2. B. endothermic
3. B. Eating a TUMS to calm your upset stomach.