endothermic reactions

photosynthesis

One of the most important series of endothermic reactions is photosynthesis. In photosynthesis, plants make the simple sugar glucose (C6 H12 O6 ) from carbon dioxide (CO2 ) and water (H2 O). They also release oxygen (O2 ) in the process. The reactions of photosynthesis are summed up by this chemical equation: 6 CO2 + 6 H2 O C6 H12 O6 + 6 O2 The energy for photosynthesis comes from light. Without light energy, photosynthesis cannot occur. As you can see in the Figure 1.2, plants can get the energy they need for photosynthesis from either sunlight or artificial light.

what is an endothermic reaction

All chemical reactions involve energy. Energy is used to break bonds in reactants, and energy is released when new bonds form in products. In some chemical reactions, called exothermic reactions, more energy is released when new bonds form in the products than is needed to break bonds in the reactants. The opposite is true of endothermic reactions. In an endothermic reaction, it takes more energy to break bonds in the reactants than is released when new bonds form in the products.

energy change in endothermic reactions

The word endothermic literally means taking in heat. A constant input of energy, often in the form of heat, is needed to keep an endothermic reaction going. This is illustrated in the Figure 1.1. Energy must be constantly added because not enough energy is released when the products form to break more bonds in the reactants. The general equation for an endothermic reaction is: Reactants + Energy Products Note: H represents the change in en- ergy. In endothermic reactions, the temperature of the products is typically lower than the temperature of the reactants. The drop in temperature may be great enough to cause liquids to freeze. Q: Now can you guess how an instant cold pack works? A: Squeezing the cold pack breaks an inner bag of water, and the water mixes with a chemical inside the pack. The chemical and water combine in an endothermic reaction. The energy needed for the reaction to take place comes from the water, which gets colder as the reaction proceeds.

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questions

only endothermic chemical reactions involve energy.

a. true

-->  b. false

in an endothermic reaction, it takes less energy to break bonds in the reactants than is released when new bonds form in the products.

a. true

-->  b. false

a constant input of energy is needed to keep an endothermic reaction going.

-->  a. true

b. false

which statement about the chemical reactions of photosynthesis is true?

a) they are endothermic.

b) they produce energy in the form of light.

c) they can be represented by 6co2 + 6h2o  c6h12o6 + 6o2.

-->  d) two of the above

during an endothermic reaction, energy is

-->  a) absorbed.

b) released.

c) destroyed.

d) created.

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