Chemical Reactions

When Hannah mixed two chemicals in the lab, an exothermic reaction takes place. Which of the following would be proof that the reaction was exothermic?

• a change of color

• a temperature decrease

• a change of state

• a temperature increase

Lily, a scientist, combines chemicals and produces an exothermic reaction. What byproduct of this reaction would show that it is exothermic?

• heat

• a precipitate

• coolness

• gas bubbles

Evelyn is conducting an experiment in her science class. Which of the following is a chemical change?

• water freezes to form ice

• gasoline burns in a car engine

• sugar dissolves in water

• a piece of metal expands when it is heated

Kai is conducting an experiment where methane and oxygen turn into carbon dioxide and water. In this reaction, the methane and oxygen are called

• reactants

• neutrals

• products

• energizers

Grace is conducting an experiment in her chemistry class. She wonders if increasing the concentration of a reactant in a chemical reaction will _____________

• decrease the rate of reaction

• increase the rate of reaction

• stop the reaction from happening

• have no effect on the rate of the reaction

Harper is conducting an experiment. Which of the following represents a chemical change?

• cutting a piece of paper with scissors

• cooling a mixture of air and kerosene vapor to obtain liquid kerosene

• burning a piece of notebook paper in the presence of oxygen

• heating water over a flame to its boiling point

Nora observed several processes in her backyard. Which of the following is a chemical change?

• the rusting of iron

• dissolving salt in water

• melting an ice cube

• bending a copper wire

Ethan and Maya are conducting an experiment in the lab. They combine two substances in a beaker at room temperature, and the beaker feels cold to the touch. This means that the substances:

• have not reacted with each other

• have undergone a physical change

• have undergone an endothermic reaction

• have undergone an exothermic reaction

During a science experiment, Anika observes that the mass of the products is always:

• slightly less than the mass of the reactants

• the same as the mass of the reactants

• much less than the mass of the reactants

• greater than the mass of the reactants

Anika is cooking pasta and notices that raising the temperature of the water would make the cooking process __________________.

• happen slower

• stop completely

• happen faster

• proceed as normal